A homemade alarm system made from two “normally closed” audio jacks is the focus of our most recent Weekend Project, the Alarm Bag. The alarm system, built into an enclosure (above), can be installed into any bag (in our project, a messenger bag is used) or even modified to act as a door or window alarm. The 2-jack design means the alarm will activate whenever the second audio jack (the trigger) is removed. It’s an interesting use of components not typically designed for this purpose, except for the 102dB Piezo siren which is an absolute screecher of an alarm!

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