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Some related (but not the same) questions:

Listening (eavesdropping) device that can be put into victim's ear? (which is closed because of the need to focus)

Microphone implanted in and powered by the body (most related, yet I want the design to be even further)

I want to design a listening device which is put into the human ear canal of secret agents in some espionage activity, and/or to eavesdrop whatever the victim is hearing. The information (voice) eavesdropped is sent remotely to the receiver or the eavesdropper of a distance. And this device should be small enough to be put into ear canal and stay there. The device is powered by human body (like charged by bio-electricity).

To make this possible we need to power both the microphone and the transmitter, sending signals strong enough to travel a certain distance and be received properly. I wonder, based on the current science and technology, how much power is required for this listening device to work, and to how far away it can send the signal for receiver to get the information. Namely, can the power generated by human body be used to make such device possible, given the conditions above? (Or what are some other handicaps?)

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    $\begingroup$ Why specifically in the ear canal (which is easy to search visually) instead of buried in the petrous part of the temporal bone, where the device would be safe from casual inspection and mechanically well-protected? Or should we understand that the device is planted without the knowledge of the wearer? Do we asume that those insensitive clueless wearers also don't wash their ears? $\endgroup$
    – AlexP
    Commented Oct 5, 2021 at 19:47
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    $\begingroup$ if your "certain distance" is a few inches no problem if it is a few miles you are SOL. $\endgroup$
    – John
    Commented Oct 5, 2021 at 21:04
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    $\begingroup$ ... why do you need to put this in the ear of your own secret agent? Presumably they could report back to you about what they heard. Why won't a "normal" audio bug - such as one stitched into clothing or some other piece of equipment - be sufficient, if recording the audio is required? $\endgroup$ Commented Oct 6, 2021 at 1:36
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    $\begingroup$ It is to be put in ear canal because, as mentioned above, one of the goal is to use the device to eavesdrop someone secretly. So indeed, it should be put into secretly. $\endgroup$
    – user90578
    Commented Oct 6, 2021 at 14:29

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This is an active area of research. A lot of people have internal electronic devices implanted like pacemakers, and scientists would love it if they could power it off glucose, and there's a lot of money going into doing this. But, we can't do it now. It's too tricky to generate a meaninful amount of power from motion or heat or glucose.

There is an already used today alternative. Use inductive charging and batteries.

Cochlear implants are a commonly used technology, and are easy to explain if detected. They're fairly close to the surface, so you can charge them with inductive charging, where you hold an electrical field close to them. A spy agency could easily redesign a phone charger to charge a cochlear implant in someone's ear without much risk of detection, or even put a charger in someone's room to do it without their knowledge while they sleep.

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