Bag movement alarm for theft prevention

In short: I developed a portable, battery powered device that sounds an alarm when your bag or purse is moved. Once armed, can only be turned off by your secret code.

The device is built off an Arduino compatible Trinket Pro, using an off-the-shelf project box with PCB.


Bag movement alarm for theft prevention

Problem I had:

When I go to a happy-hour or a cocktail party, I often have my computer bag with me. But I do not want to carry it around with me, so I put it down somewhere, hoping that no one takes it. I may check on it periodically, or stand so that my bag is in my view, but I am still concerned someone may take it. Or I may be traveling, taking a nap at an airport or when waiting for train and be concerned that it might disappear while I am sleeping. Or any number of circumstances in my life where I need to protect my bag from being stolen.

Solution I built:

I built a small, portable alarm to warn when my bag has been moved. It is 9V battery operated, but without an on/off switch, otherwise the potential thief could just hit the off button. As a result, I have an ‘arm’ button, and then you have 20 seconds to but the bag/purse + device stationary. After being armed, if the bag/device is moved for more than 5 seconds and above a threshold level, it sounds an alarm until the correct code is entered. The secret code uses a 4 button interface, but the code can be any length.

Genesis / special motivation:

My parents were recently traveling abroad, and their bag (with their camera) was stolen while they slept. I decided to build this for them for a Christmas present, so that they would not have to go through that again. I was thus forced to build this over the course of December, which was great motivation.


If you want more info on how I made this:

I also blogged about making this (and the challenges I faced along the way) on my personal blog at

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