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Assume a low-tech scenario, no Electricity, more or less iron age tech-levels.

Some people in this world carry devices the size of a modern compass. Within is a very thin (like hair, but of lighter color) wire, which is normally straight but bends in the presence of certain dangers (more or less radioactivity).

NOTE: Somehow you can see the wire and its state day and night with the naked eye, so that's not the problem. The function is also not impaired by the devices rotation etc.

That's all fine and dandy, but how would they notice without paying close attention 24/7? I do not know a way of translating this very small movement to something which would alert a human, much less so when sleeping.

Are they doomed? Do they have to stare at the device (at least one of the group) all the time, or is there a low-tech-way to "amplify" the warning?

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The general answer is that you want a trigger. You have a source of potential energy that is held at bay with a tremendous amount of mechanical advantage. When the trigger is moved out of the way, the potential energy is released.

You would probably need at least a double-layered trigger. You'd want a very fine trigger which responds to the hair's movements which merely releases the energy need to trip a second trigger. That second one empowers any number of devices which could be used to alert someone (literally too many to mention. Hand me a beer and I'll reel off 1,000 of them. You'll have to pay me $20 if you want 10,000).

The hard part is the part not stated in your question: how strong is this hair's movement? We can make mighty fine triggers, but as you start to approach the forces measured in small numbers of ounces, it gets harder to make the system work without accidentally going off if shaken. (For perspective, firearm triggers are on the range of 1 to 12 pounds of force. Too low and the gun may go off accidentally. Too high, and accuracy theoretically suffers).

One trick you could do to solve this is to leverage chemistry. You could find a pair of compounds that react (such as baking soda and vinegar), put one on the hair and one to the side so that they touch if the hair curls. You can use this reaction as a "trigger," and use it to fuel the larger trigger to cause someone to awaken.

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    $\begingroup$ It may be a good case for a hybrid strategy. Have it watched continuously while it is being moved, but arm a trigger mechanism when it will be stationary, and unlikely to be shaken, for a while. $\endgroup$ – Patricia Shanahan Aug 26 at 3:14
  • $\begingroup$ @PatriciaShanahan Thanks! Thats exactly what I will do. Nice addition to Corts answer. $\endgroup$ – openend Aug 26 at 7:46
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    $\begingroup$ For the fine trigger you could look into "hair tension hygrometers", where the slight variation in humidity of a hair moved a lever to mark it in a scale. You could make that the lever throws a weight into a bell or something like that. $\endgroup$ – Carlos Martin Aug 26 at 9:56
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    $\begingroup$ The problem is almos exactly the same as triggering an alarm from a fine clockwork mechanism. The forces moving the hands of a pocket watch are also very small and could accidentally fire. But small watches with alarms were developed in a variety of styles and will provide many options to reduce shock and prevent accidental triggers. $\endgroup$ – Falco Aug 27 at 8:05
  • $\begingroup$ An accidental trigger now and then would probably also be ok and give some additional jump scares for the story. When the alarm goes off, the user will have to take out the device and look if the hair is actually curled. If not, he will flip a switch and rewind the alarm. $\endgroup$ – Falco Aug 27 at 8:06
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This low tech alarm that lights up the room on triggering. It is in the British Museum.

enter image description here

enter image description here

When the target time is reached, or your wire bends, a trigger causes a flint-lock mechanism to light some gunpowder. A candle initially has its wick in the gunpowder, but a clockwork mechanism lifts it up with enough delay to allow it to light.

That gives both an audible alarm (the bang when the flint hits the striker and the gunpowder lights) and a light from the candle.

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  • $\begingroup$ Unfortunately, this does not mix well with my quasi-iron-age. If they have gunpowder, they will have guns, and that's the last thing I want :) $\endgroup$ – openend Aug 25 at 23:22
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    $\begingroup$ No. The Chinese had gunpowder for several hundred years and used it for fireworks but nerver build guns (AFAIK) $\endgroup$ – Julian Egner Aug 26 at 9:31
  • $\begingroup$ Yes, that's true afaik. But the roman's did not :) $\endgroup$ – openend Aug 26 at 10:35
  • $\begingroup$ @openend Substances other than gunpowder could also be made to work for something similar. $\endgroup$ – Makyen Aug 26 at 17:18
  • $\begingroup$ @Makyen Maybe combine this with the chemical reaction idea. $\endgroup$ – Patricia Shanahan Aug 26 at 17:40
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With a bit of low-tech surgery, you attach the thin wire to the skull of a canary, such that when the wire bends, it pokes the canary in the eye. Removal of the eyelids is probably necessary.

Alternatively, you might be able to attach this rig to a Venus Fly-Trap, but they don't make as much noise when they get poked. Still, it might be enough for the first stage of a multi-part trigger.

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    $\begingroup$ what the hell. I don't actually think that you would need to have it directly poke it in the eye. I think something more feasible would be to insert it underneath someone's skin. $\endgroup$ – wpokdljnlnmn Aug 27 at 4:46
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it is the size of a pocketwatch so use simple clockwork, basically you are building a spring driven vibrator (which is just an uneven spinning weight) that uses the wire as the release mechanism, (just like a bimetallic strip trigger) iat rest the strip holds back hte spring when it flexes it releases the mechanism just lake the catch on a spring loaded lid or the escapement on clock. Sure you have to wind it up after it goes off but so what.

You can make it noisy or quite, attack a bell ( or just lace it in a metal bowl by your bedside) for noise or use the vibrator for quiet. Its quiet and yet still hard to miss. Why would you want it to be quiet. You don't want something that announces your presence to the enemy after all.

If you are not worried about actual timekeeping pocket watch mechanisms are not that hard to make so it is easily with available technology. The romans could build this device without issue.

enter image description here

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