Thwart Bike Thieves with a Shock-Activated Lock

If you don’t want your bike stolen, the best way is simply to lock it up. YouTuber GreatScott!, however, has figured out how to add an extra layer of security to his two-wheel ride with a DIY alarm. While there are many ways to build something like this, his rig is able to detect unauthorized vibrations, and emit an annoying sound without even using an Arduino or similar.

To pull this off, GreatScott! implemented a piezoelectric disk that gives off a small voltage when hit, using a differential amplifier circuit to increase this to recognizable levels. Instead of an Arduino-style board, the decision to beep is made with the help of a comparator and flip-flop. When activated, the flip-flop triggers the buzzer via a MOSFET, causing it to produce a piercing noise. This can eventually be turned off by a pushbutton, and there's also a main power switch to cut it off altogether.

The device is theoretically able to run for 135 days on its 1200mAh LiPo battery, so you could park your bike for quite some time before would-be thieves can simply “wait it out.” One might note that a potential thief could simply flip the switch to off, or perhaps smash its 3D-printed case, but obviously this person wouldn’t know what was actually going on before garnering unwanted attention.

Although it might not secure your bike by itself, something like this when combined with a lock could be enough of a deterrent to make someone think again before snatching.