Electronics > Open Source Hardware

Contemplating opensource alarm system

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libralect:
This is my tripwire method!!! It's the cheapest, most robust motion based alarm, which uses no energy until triggered!!! it's 20 grams in total if you wanna loud invisible micro-alarm on a bike. It can be sized up to a 500dB train-horn.

The tripwire works by jamming the switch of a very loud piezo/horn using a plastic card like a plexus, and using nylon fishing line to snag the card to something you don't want displaced (a bike), or to make a tripwire in your house.

1/ Put a very loud piezo or a horn on a battery / DC circuit.
2/ make an interruptor switch with spring metal which can be jammed with a plastic card
3/ measure a length of Nylon that you can attach to a bike wheel or in a tripwire and snag the plastic card

It's that easy! when someone walks in your perimiter zone, the invisible nylon will pull the plastic card in the interruptor and the piezo/horn will sound at 100-500dB whatever you wish is.

You can even put it in the saddle of your bike, so that it beeps at 120dB if taken.

Nominal Animal:

--- Quote from: libralect on October 05, 2022, 05:36:03 am ---It can be sized up to a 500dB train-horn.
--- End quote ---
500dB? It's an exponential scale.  A shockwave peaks at 191dB in standard atmospheric pressure, where the low-pressure regions become a vacuum.  500dB involves 2100 ≃ 1030 times that much energy; with high-pressure peaks of 1015 atmospheres, or around 40 million times the pressure at the center of Jupiter.

A train horn actually producing 500dB would need to be powered by antimatter, and you need a Kardashev type II civilization to be able to build one.

jpyeron:

--- Quote from: Nominal Animal on October 05, 2022, 08:13:56 pm ---
--- Quote from: libralect on October 05, 2022, 05:36:03 am ---It can be sized up to a 500dB train-horn.
--- End quote ---
...
A train horn actually producing 500dB would need to be powered by antimatter, and you need a Kardashev type II civilization to be able to build one.

--- End quote ---
:-DD, but it would also need to be UL listed.

Nominal Animal:
I don't think UL has standards for planetary obliteration weaponry.
(The "500dB" train-horns you see on eBay and such is just a ploy to attract gullible buyers.  They can be anything from 40dB (toy) to 110dB (real).)

If I were to build an open-source alarm system, I'd make it into multiple independent circuits which monitor each other, all messages encrypted, and disarm messages additionally using salted hashes of the passkey (derived from the user "password").  This way, each monitoring circuit knows only one or more salted hashes of the disarm message key, not the key itself.  I'd also add purely passive monitoring circuits, recording (write-only) all trips, disarm attempts, and successful disarms.  Simply put, a distributed interconnected system favouring one-way monitoring connections.

The main thing, for me, would be to avoid single point failure scenarios.

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