This project uses simple electronics to create an alarm circuit for a shoulder bag. The key components are two 1/8″ headphone jacks with “normally closed” switches, which detect whether a plug is in the jack. Wiring two of these jacks in series with an alarm creates a circuit that activates when both plugs are removed. With this arrangement, you can use one jack to keep the alarm from sounding while you arm the system. The other jack accepts a plug that you can tether to a belt loop or other anchor. When the bag is pulled away from its anchor plug, the alarm sounds. You can of course use this same circuit for a handbag, backpack, or any other personal cargo carrier.
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