# Is using thermal energy an effective method to powering an implanted tracking device?

So in this world somewhere in distant future. The government has created I.D Chips that are designed to be biologically implanted into its own citizens. To ensure extra "security" and also act as a single account for banking, job applications, account managing,etc.

The Main part of the chip is attached to the wrist and can easily be seen with a metal hexagon sticking out of the skin.

Though underneath, the chip has mechanical roots designed to monitor all the actions of the individual. [Like running, sleeping, swimming, etc.] It also contains a tracking device to ensure where the citizen is at all times. If the citizen were to grab a knife, cut the skin and attempt to pull the chip out, the chip could send a shock through the whole body. Though I came into a problem is how to power this device.

Could having the device dependent on the bodies thermal energy allow this device to perform all the functions mentioned above?

• Re: "the chip could sense a shock": Do you mean it could send a shock? Oct 29, 2017 at 18:01
• Monitor all actions, tracking device, controls behavior... So, this device is basically like an Apple Smart Watch? Oct 30, 2017 at 8:30
• So it seems GPS is too power hungry for a self powering tracking device. Do you need GPS or some kind of blip that can be detected by nearby checkpoints/officers? Perhaps look into Wireless Power Transfers to help solve the battery issue. Also batteries do need replacing as they degrade over time. Oct 30, 2017 at 11:57
• Thermal power? no. not enough temperature difference. But it's embedded in your blood, why not just have it run on your body's energy? a fuel cell running on glucose from the blood, and oxygen from either your blood or the environment, would be quite strong enough.
– user79911
Nov 20, 2020 at 19:24

It also contains a tracking device to ensure where the citizen is at all times.

GPS uses frequencies around 1.2-1.5 GHz. According to this you lose 4dB/cm in RF power when going through people/meat, thus your antenna must not be buried too deep. In fact, it would be better if it was right under the skin.

Thus the best place for GPS reception would be on top of the cranium. Sorry Will, if you put it down there, you won't get any signal... 1.5 GHz won't go through the body, it will be absorbed.

The obvious counter to this is to wear a tin foil hat, as everyone already knows.

Other places would be on the shoulders, for example.

Now, your tracker has a few issues, because GPS reception is unreliable: it doesn't work well indoors, doesn't work at all in tunnels, and especially not in the rebels' secret underground bunkers that you want to find.

Thus "loss of signal" will occur often, basically every time your faceless minions walk into an underground car park or even indoors.

Thus you can't differentiate between "loss of signal for legal reasons" and "someone put a tinfoil hat, send in the SWAT teams" which makes your tracker less useful.

Also, unless you want to bolt self-aligning satellite dishes on top of everyone's head, the receiving antenna will be tiny, perhaps like the one in a smartphone. Unless you shoot a whole new constellation of satellites into orbit with much higher RF transmit power than what the current GPS ones have, this tiny antenna means the received signal to noise ratio is very poor, and thus the GPS chip will need at least several seconds of averaging to get a proper location fix.

The limits to this are about the amount of power received by an antenna of a certain size versus ambient noise, and this no amount of space magic will give you a better time-to-fix unless the transmitters are made a lot more powerful.

We do it this way for cost: powerful RF transmitters require power thus big solar panels, which are heavy, which require bigger rockets to shoot them into space, which costs money. Maybe no-object once you Take Over The World, but keep this in mind.

So, with current GPS RF power levels you'll need to power up your GPS receiver for quite a while before getting a fix. This means it will use more energy than you think. Having a look here, it will draw 60mW for a few seconds during acquisition.

Also, acquisition requires a much higher signal strength than tracking, it won't work at all indoors while tracking might work if the "user" is close to a window.

The datasheet I linked helpfully describes the modules' logging features, and how to conserve power in a data logging application, but if you want real time logging, less than about 15mW average won't cut it.

And you need real time logging, at least every few seconds, if you want to know where the entrance to the secret rebel hideout is!

This power draw is a problem. Your chances of fixing it with space magic technology are low, because the underlying circuitry will have to include a few RF circuits which are analog and include some hard tradeoffs in the noise versus power draw domain. Even if it's much lower, say 2mW, you still need to transmit often enough, which rules out a thermal generator, as said in the other answers.

However you can always handwave a space battery to power it, or a graphene supercapacitor, whatever.

Every one of your minions must recharge their implant every two days. A routine search and interrogation will also be performed on the occasion, of course. Remember to always be nice to your political officer. They're here to help!

Shocking the user when the implant stops working or is removed doesn't seem doable. It would be a lot better to release a chemical if the implant is tampered with, or the user "forgets" to report to the nearest office of the Ministry Of Truth for his recharge. Effects of said chemicals are up to you, from giving the users' skin a fluorescent green glow (which gets them arrested) to making them sick. Lots of plot bunnies here.

• I have absolutely no idea about signal strength and power requirements, but wouldn't it be much easier to use senders located on the ground? They are much easier to maintain, trivial to power and multiple can be used like GPS for a position-fix. Cellphones do that, hence the name.
– JFBM
Oct 30, 2017 at 0:34
• Let's not forget bio-electric or peristaltic sources of power.... Oct 30, 2017 at 1:21
• @J_F_B_M yes (like cellphone towers) however these won't get you very accurate positioning. GPS works by calculating the propagation time (hence distance) from the receiver to the satellites, in a straight line of sight... this is possible because the satellites are in space. So if you stand somewhere with open sky above you (even a street, as long as it's wide enough) there will be a straight line from you to a few satellites, 3 sats give you a fix, 4 sats give you altitude, more give extra accuracy and update rate if the receiver supports it. Oct 30, 2017 at 10:11
• Cellphone signals however come from towers which are at low altitude, so they reflect and scatter a lot on ground features and buildings. It is possible to calculate the propagation time, but it may include extra length as the signal bounces and scatters on buildings etc. Unless you have a direct unobstructed line of sight the path length measured will be all over the place, and so will be the location. Oct 30, 2017 at 10:14
• Same for recent efforts at location via triangulation: if you have good signal strength from one tower, it may not be the closest one at all, it could be that you stand in front of a window and have an unobstructed path to a tower far away, while a much closer one, on the other side of the building, is obstructed by the building itself... or a hill... techdirt.com/articles/20140908/04435128452/… searchengineland.com/… Oct 30, 2017 at 10:16

Using thermal energy for power generation is a thing, but you need a temperature difference to make it work. You implanted device is likely to be essentially uniform in temperature meaning that it won't be able to generate any power this way.

Even if you do have a minor thermal gradient you can't get much from it. The Carnot limit sets the maximum possible power to the thermal energy flowing across the gradient times an efficiency given by $$\eta = \frac{T_\text{high} - T_\text{low}}{T_\text{high}}$$ (with the temperature expressed in an absolute scale where zero is absolute zero). For the small thermal gradient available to an embedded device both the raw flux and the efficiency will be very small, so the available power is vanishing.

If you want to diddle the biology in hopes of changing the answer you should note that you restrict the part of the anatomy where the thing will work to the part with a steep thermal gradient.

Let's do an estimate of how much power would actually be available.

Assumptions:

• Working area of $1\,\mathrm{cm^2}$.

• Thickness $1\,\mathrm{mm}$. We might make the device thinner, but then it won't be able to use the full thermal difference available.

• We place the power-generation zone between the muscle and the top of the dermis/bottom of the epidermis (which gets us fairly consistent temperatures over a range of external conditions: don't want to be at the mercy of the weather for this thing to keep working ) And we'll pretend we get the full nominal core temperature to skin temperature difference: $34$–$37^\circ\mathrm{C}$.

This is rather more than a little optimistic (especially as thin as I have proposed to make the device), but let's go with it.

• Perfect Carnot efficiency. (Note that this is a really big ask: the current leading solid state technology for this get about 1/6 of the theoretical maximum.)

• Selecting a thermal conductivity is the hard part. A higher value results in more heat flow if the source region can be replenished and the waste heat rejected fast enough; otherwise the temperature difference drops as the hot end cools or the the cool end heats up (or both). So we use a value close to that of flesh: $k = 0.5 \,\mathrm{W/(m \cdot K)}$.

The available thermal power is then \begin{align*} P_{th} &= k A \frac{\Delta T}{\Delta x}\\ &= \left(0.5\,\mathrm{\frac{W}{m \cdot K}}\right) (10^{-4}\,\mathrm{m^2}) \left( \frac{3\,\mathrm{K}}{10^{-3}\,\mathrm{m}}\right)\\ &\approx 0.15\,\mathrm{W} = 150\,\mathrm{mW}\;. \end{align*} That's pretty low, but if we're assuming a lot of technological advance it might not be disastrous. After all a 3G phone can transmit with only about $750\,\mathrm{mW}$.

But now let's look at that Carnot efficiency (recalling that we have to use absolute units here): \begin{align} \eta &= \frac{(310\,\mathrm{K}) - (307\,\mathrm{K})}{310\,\mathrm{K}} \\ &= \frac{3}{310} \\ &\approx 0.01 \;. \end{align} So the actual power available in our highly optimistic model is around $1.5\,\mathrm{mW}$.

That's awfully low for something that is suppose to keep tabs on the wearer and we've made a lot of highly optimistic assumptions to get it that high. Image what happens if we let that temperature difference sag even a little bit. Or we have to make it thicker to access the full temperature difference. Or we can only get halfway from where we are now to the theoretical best efficiency.

• It isn't a lot of power, but I don't think it's completely unrealistic. For recording pulse etc., you only need a couple of analogue FETs and a very low-clocked microcontroller with a small CMOS SRAM. That should be doable with 1 mW and still leave something to charge a big capacitor so we could every half-hour or so boot up the GPS receiver and write the data to bigger flash memory, and every day send a digest to the Ministry. Oct 29, 2017 at 12:22
• The real question would be how big of a capacitor you would need to embed to permit the "If the citizen were to... attempt to pull the chip out, the chip could sense a shock through the whole body." Doing this to stop a determined citizen (i.e. one that would take a knife to their own body) would require a lot of stored power, and all they need to do is hold a piece of styrofoam over the heat-sink (and perhaps put on a sweat shirt) to massively limit its ability to recharge. Oct 29, 2017 at 14:04
• @leftaroundabout: You may want to do the math on that. The problem with GPS is that it operates at a negative signal-to-noise ratio (!). That's not a theoretical barrier, but it means you need a lot of signal analysis, and also a lot of signal. And running GPS only infrequently makes it worse as GPS satellites must be reacquired. You'd be better of with cell phone tower triangulation, offloaded to the cell phone network. Oct 29, 2017 at 23:24
• How does it look if, instead of a fully internal device, one end is exposed to air in order to get a better gradient?
– Eth
Oct 30, 2017 at 11:24

Could having the device dependent on the bodies thermal energy allow this device to perform all the functions mentioned above?

Well, I think you are OK up until it starts shocking the person. Thermal energy produced by the human body is not a huge source of power but it is something that is being explored today. As example, Dr David Carroll, Wake Forest University, has published research on this topic. I'm not sure how your device would gather this power. Having only a small area, the wrist, to work with would limit the amount of heat it can absorb and that limits the power it gains.

However, there is nothing that says the power comes only from one source. I'd like to suggest some other possibilities.

First, harness kinetic force. When walking, most humans will swing their arms in counter force to the movement of their legs. Have your device include a bit of hardware akin to a shake flashlight and the simple movement of the swinging arm could give some power. The shake light is just an example. A better example, pointed out in the comments by Joe Bloggs, is a watch powered by body movements or a kinetic watch. Your device would most likely have a more refined generator, it may not make a huge amount of power but it would help.

Next, harness the power of flowing blood. Your device "has mechanical roots" and why would those roots not monitor blood flow? And while you're there, why not harness the blood flow? Researchers in Lucerne, Switzerland are doing that today. Just like the others, this isn't going to produce a lot of power, but again, every bit helps.

Finally, looking to today's tech for inspiration. We have pads that you can drop your phone on and it charges the battery. You could extend that idea and give it range greater than contact. Power could be broadcast, transmitted, directly to the device. This may even be the main method of charging internal batteries with all the others providing backup/supplemental power.

• +1 for the kinetic option. We use it for watches nowadays, so it’s really not a massive stretch. Oct 28, 2017 at 22:08
• @JoeBloggs, watches use miniscule amounts of power -- in the nanowatt to microwatt range. A thousand-fold increase in power generation is a massive stretch.
– Mark
Oct 29, 2017 at 17:39
• Harnessing the power of flowing blood - this sounds ruthless, efficient, hard to remove and sort of evil. Exactly what we'd want for the kind of mass-surveillance state that would impose such devices. They could also use oxygen and nutriments from said blood as a power source as well.
– Eth
Oct 30, 2017 at 11:26
• @Eth I always feel that a technological dystopian oppressor should never do things in half-measures. If you don't mind I may use your idea :) Oct 31, 2017 at 0:09

# No.

For thermal power you need a cold thermostate where the heat goes. From 37 °C to 25 °C ambient you can perhaps eke out a couple mW using a Seebeck plate (Peltier cell in reverse), no more; unless you mount a radiator on everybody's back.

# Power

A much more promising source of energy is blood. Basically, you divert a small quantity of blood through a fuel cell, where the oxygen-poor environment prompts haemoglobin to release oxygen. Burning that oxygen with blood glucose yields power, water, and CO2; the blood will zealously get rid of the latter two.

How much power you can absorb: you can surely absorb as much energy as a medium-sized muscle group. The blood already supplies sugar and oxygen to such. The effect will be a slightly increased basal metabolism. The body requires about 25 small calories (0.0231 kCal) per second, corresponding to roughly 100W.

A Samsung S8 runs at least 24 hours with a 13.48Wh battery, therefore 0.56W average are enough to keep it running; indirectly increasing metabolism by 0.5% due to increased consumption isn't even going to register.

Of course, the implant may become a problem with people with vascular problems - but a thermally powered device would also work haphazardly in people with low metabolism, or living in very warm climates, where the temperature differential is less.

# Location

Locating the device via GPS doesn't seem a very good idea to me. Access to GPS signal is poor, and you need anyway to re-transmit the location to the central servers. So, given that you need a data connection, why simply not triangulate it? Include a very high-precision timer in ground stations. When they receive a signal from the chip, they note the arrival time, and by comparing the arrival time between themselves, three or more cells would be able to exactly pinpoint the chip itself.

I believe this can be done today to precisely locate a telephone, whether its GPS is active or not.

# Purposes

The same mechanism that supplies the power can, with small modifications, be tuned to detect any of a plethora of chemical substances, markers and antigenes.

There is actually talk of a programmable carbon nanotube matrix capable of running almost any chemical test for the presence and titration of substances in a solution.

So your gadget could precisely monitor one's health status and warn if, for example, cancer antigenes abruptly popped on its radar. Of course, it could transmit also data about hormones, alcohol, neurotransmitters etc. and detect drunkenness, substance (ab)use, arousal, fear, rage and so on.

# Placement

For logistical reasons it would be probably implanted more centrally than the wrist (less chances of accidents and no problems with amputees), and it would be completely inside the body. Possibly it could be placed behind, or partially inside the xiphoid process, with the fuel cell close to the celiac artery.

Since it's there, it would be relatively straightforward to hook it to the central nervous system. As any dentist could tell you, a very weak current in the right nerve can make it feel like half your body is on fire, making it a very efficient anti-tamper system.

For any thermal-powered device, you need both a hot source and a cold sink.

Something embedded in the body will only have to body temperature. Since you have an external component as well, it is perhaps possible to use the internal vs. external temperature difference as a power source. This would work best when the outside temperature is cool, but would be useless when the outside temperature is the same as body temperature.

So, it could not ever be a reliable power source, but perhaps backed by internal power storage might be useful.

Typical external temperatures preferred by humans are somewhat cool compared to body temperature, but not significantly so. So a thermoelectric generator would have quite limited efficiency, but it is the most likely form of generator for your proposed usage. For something on the order of the proposed device, averaging 1 milliwatt of power would be very challenging if possible at all. The external stud will tend to be near body temperature because the amount of heat it can lose to the environment is quite limited.

Any device that is embedded in the body and is also externally available is a real problem due to infection, and requires careful and regular maintenance. So it is not practical unless this is the only reasonable form for such a device to work.

A far more practical arrangement is for the device to be powered by an external EM field when it is needed, exactly like a passive RFID chip. Given you want 24 hour operation, it would only be necessary for backup power within the device and charging at night just like your cell phone. Low reserve-power could just trigger an alert that you must correct to stay in compliance with government regulations.

One bio-source I have never heard of anyone using (ethical considerations come to mind, and installation would be more complex than most potential sources) is installing a small wind-turbine perhaps below the trachea. Breathing uses about 1 watt of power, so siphoning off a few milliwatts should be comparatively easy, which makes this a high-power source. Since this is below the esophagus, you would not have problems of clogging related to food and drink consumption.

• Instead of an EM field, I'd go for the same mechanisms used in "perpetual" watches (which are really powered by the motion of your forearm). Oct 29, 2017 at 0:15
• @RonJon -- Perpetual watches are good too. Not as energy dense, but pure bio-powered. Oct 29, 2017 at 1:55
• Any obstruction in the trachea makes the accidental inhalation of food or drink much more dangerous. This happens pretty regularly - a few times a year for most people, at a guess. Oct 29, 2017 at 14:07

Yes. But not in the wrist.

As has been pointed out, to power a device with heat one needs a hot side and a cold side. Fortunately, for half of the human populace, there exists a place in the body that is maintained at a cooler temperature than the rest of the body: the testicles.

https://blogs.scientificamerican.com/bering-in-mind/why-do-human-testicles-hang-like-that/

Fortunately, human scrota don’t just hang there holding our testicles and brewing our sperm, they also “actively” employ some interesting thermoregulatory tactics to protect and promote males’ genetic interests. I place “actively” in scare quotes, of course, because although it would be rather odd to ascribe consciousness to human scrota, testicles do respond unintentionally to the reflexive actions of the cremasteric muscle. This muscle serves to retract the testicles so they are drawn up closer to the body when it gets too cold--just think cold shower--and also to relax them when it gets too hot. This up-and-down action happens on a moment-to-moment basis, thus male bodies continually optimize the gonadal climate for spermatogenesis and sperm storage.

Rather than the wrist, your future society could implant their devices in a place in close proximity to the testicles to facilitate their use (or use of the scrotum) to expel heat. As long as the temperatures produced are not too radical, the scrotum will simply use its normal methods to keep contents cool when it is hot.

As regards the prospects of tracking women (who are usually without scrotums) this becomes more tricky. I observe that all women I have observed breathe continuously, with air (almost always below ambient body temperature) moving through a series of passages on the way to the lungs. Some of these passages act to warm the air; the passages of the nose have exactly this function. A heat exchanger placed in the nose - perhaps a hollow tube permitting the passage of air - could be cooled by this passing air and so allow the temperature differential needed to power your device.

• I observe that all women I have observed breathe continuously -- that's some pretty serious sampling bias, if you ask me. Also, there's a tautology in there that seems suspect. I think a citation here would strengthen the answer ;-) Oct 28, 2017 at 22:42
• While clever sounding, this is mostly nonsense. The temperature difference is not sufficient to get a usable amount of power. Oct 29, 2017 at 0:54
• The problem isn't getting a temperature difference: you can have that across the skin at any point in the body. It's how small that difference is. See the calculations I've added to my answer for how that kills you. Oct 29, 2017 at 4:44

Depending how ubiquitous the trackers are, you don't need a lot of power. Passive RFIDs work from a couple meters and so having detectors built into light posts, vending machines, stop lights, entrances to public buildings would catch most people on a very frequent basis.

A class of active/passive RFIDs uses battery to transmit, but only responds when it gets pinged. A thermal device that generated 1mw but charged a capacitor would allow for burst power use much higher.

Longer range active tracking (the device broadcasts on a regular interval) requires more power, and one that sends the actual location also requires GPS which is very power intensive. (There's a reason your phone dies fast when using a mapping function.)

But why thermal? Blunt force: Put it the foot and it make it generate power piezoelectrically with every impact. Put it in a tooth. Attach to two body parts that move past each other. Tendon in tendon sheath. The installation is more complex. A simpler one is embedded in a muscle and generates power every time the muscle contracts and squeezes the device.

The easy way is with a passive RFID. Ping them with a burst of microwave, and they use the power of the microwave burst to send back a few bytes of information. You put RFID readers in the entrances to public buildings, transportation centre.

You can put multiple RFIDs on the same device. Some can only be read from a couple cm away. Some can be read from a hundred feet or so.

Your society could have tiered tags. Everyone gets a passive tag shortly after birth. This will be sold to the masses as a way of preventing kidnapping, and finding lost kids. As an ID it confirms who you say you are.

If you get in trouble with the law, then you are fitted with a passive active tracker. It can be detected from further away. If you are a criminal, you may have a fully active tracker similar to the anklet devices used.

Note that spoofing an RFID is fairly easy. If I'm a Black Hat if I wrap the part of my body that has the tag with a piece of metal, then the signal is mostly blocked. If I make a duplicate tag that a confederate moves with him, then I can establish an alibi in the system for being somewhere else. If I make a thousand copies of my tag and stick them to people's clothing, then I'm everywhere at once.

With more power you can overcome these limitations. Every device (has to be more than an RFID now...) has a public and private key pair. The private key is hard coded into the chip. The public key and the identity are kept by the government. When pinged, the id number is returned in clear, a few bytes of random noise, the id number and the current time are encoded by the tracker using the private key. This message is picked up. If the watchers aren't concerned about this person, the encrypted part is ignored. If they are interested in you, or if this is a transaction, then your id number is used to fetch your public key, it's used to decrypt the rest of the message, and it needs to be close to the current time.

Note that you could also use some form of induction charger. If the device is in your finger tip, then every time you ID yourself for a transaction, your device's battery is charged up. If you go for days or weeks without buying anything you become noticed.

This becomes a common device for computer access. For locks. If the reader/chargers are cheap, they are used everywhere.

Ignoring the power-from-heat part of the question, which is already answered pretty well, I thought it'd be interesting to perform a reality check on some aspects of the idea.

The government has created I.D Chips that are designed to be biologically implanted into its own citizens. To ensure extra "security" and also act as a single account for banking, job applications, account managing,etc.

... the big think such a chip would do is provide "identity" functionality. While your question implies that you're thinking more of "ID card", identity, especially with an online component, is so much bigger. Like in Justin's answer, an RFID or NFC chip, like the ones used for pets fits the bill, but there's one additional piece of functionality I'd add - make it a smart card, able to sign documents and provide online authentication.
It's unclear if "single account for banking" means "only one bank account", which only makes sense if you (effectively) have one bank.

The Main part of the chip is attached to the wrist and can easily be seen with a metal hexagon sticking out of the skin.

You don't want the implant to breach the skin. First off, doing so might cause it to get caught on something and accidentally get torn off (which might be a plot point, but would make for some pointed questions if you had an anti-tamper feature). If the body didn't push it out on it's own at that point, anyways. It's also a great way to cause an infection. You want the implant completely under the skin. Depending on how big it is (current ones are the size of a grain of rice), it might be visible through the skin, however.

Though underneath, the chip has mechanical roots designed to monitor all the actions of the individual. [Like running, sleeping, swimming, etc.]

Activity monitoring is doable to some extent. Note that you may not be able to tell what activity is going on, just level of activity (say, if I'm swimming just by kicking my legs).

It also contains a tracking device to ensure where the citizen is at all times.

This is more difficult than it appears. The primary problem is power consumption (which the other answers have mostly covered), but the underlying issue is transmission. For example, GPS on my phone only does me any good because I can look at it directly; anybody else who wants to track my location needs to add a transmitter they can pick up. It's unlikely you could pick up a citizen's location from a satellite, but RFID chips can be read from a distance - up to 100 meters, depending on the type. In theory you could replace cameras on street corners with RFID readers (possible plot idea - "invisible" people without chips). Note that the extremely short range (~4cm) of NFC is considered a security feature, so best bet is some sort of hybrid device.

If the citizen were to grab a knife, cut the skin and attempt to pull the chip out, the chip could sense a shock through the whole body.

So mundane. Why taser your citizen, which takes a lot of power?
There's a few things here. First, especially if the device is under the skin, few people are going to want to cut into themselves, especially since it hurts. And depending on where it ends up in the hand, they may have to worry about permanent maiming. But what I'd do, if the tech permits, is to hook it into their nervous system - if they try to remove it, just stimulate the nerves.

The technology to do your data collection pretty much exists today. Once you strip away a smart phone battery, touch screen, and case, there is not much left. Your main power consumption, however, would be in the on-line real-time tracking. This, I presume, would require some form of electromagnetic transmission, which is very power intensive.

The identity stuff could be done by RFID tags, which require no internal power at all. The power comes from the external reader. If you want just a local data readout from a monitor, power for the data dump could come from the reader itself, using RF charging at the time of read-out.

The shocking part could be handled by a high-capacity Li-Ion battery that discharges all at once. The battery could be used for ONLY this purpose, thus it would not discharge until needed. Require a citizens to do an annual 'physical' which would also ensure this battery is kept charged. Tampering with it, of course, would be like tampering with ANY li-ion battery - immediate short and very high temperature fire.

So your main concerns are wireless communication for tracking, and power for data collection. For this, you would need more than just a localized power source. I would suggest either artificial photosynthesis biologically implanted in every person, solar cells implanted on the head (no head covering allowed), or some form of thermal generator.

The best bet for thermal energy would be nano-thermo-generators that line the nasal cavity, and use the temperature differential between internal body temperature (37 degrees Celsius) and ambient temperature of the air entering the nose (depending on the local of your country, average 25 degrees Celsius) for a temperature differential of 12 degrees Celsius. Since the body is doing its best to HEAT the incoming air up, here is perhaps the best bet for the body to keep UP the temperature gradient. However, I think you would be hard-pressed to get enough energy to power a cellular signal Energy Consumption in Android Phones when using Wireless Communication Technologies

In [6] Balasubramanian et al. showed that data transfer of 50 KB when using 3G needs 12.5 J, while when using WiFi the same data transfer consumes 7.6 J of energy

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There are all sorts of energy sources in the body, an excellent article in Ars Technica from a few years ago covered a few main contenders according to the current science of the time: a nanowatt from electrical potential in the ears, a microwatt from kinetic energy, 40 microwatts from a biocell using the blood's own glucose, while sweat and tears also have some potential.

Can a device do all the things you want? Sure, depending on the implementation. Depending on the sophistication of an implant, it may require far more invasive implanting to monitor all actions. Computing power and/or transmission power required for tracking may be minimised by having an extensive network of receivers instead.

However, the reason to not do this is simple: there are better alternatives. Wanting to deliver a shock requires stored energy for a quick burst of power rather than relying on a large amount of continuous energy, so it would make sense for your devices to have a battery, and this makes sense for the other challenges too. Even the batteries of the near future may be quite compact and capable of high-speed charging, so having a long-term battery in the implant that is discretely recharged through various techniques (mainly thinking wireless charging) is probably the way to go. If a battery gets below a certain minimum, dispatch agents to brush a charger against the unknowing citizen at an appropriate time if you don't already perform "checkups" on the implant on a regular basis.

The battery then acts as a buffer to the same problem: if it isn't charged, can it use body heat as a backup? Sure, but not for continuous function if it's demanding high-power features such as transmitting its precise location in the middle of nowhere. At this point, the device can go dead and build up a charge for spurts of continuous function, or act in a more limited manner by giving 'pings' on a regular basis, such function could even be remotely selectable.