Motion Activated Alarm For Your Bag


Many of us carry around a bag with our expensive personal belongings. It can be a pain to carry a bag around with you all day though. If you want to set it down for a while, you often have to try to keep an eye on it to ensure that no one steals it. [Micamelnyk] decided to build a solution to this problem in the form of a motion sensing alarm.

The device is built around a Trinket Pro. The Trinket Pro is a sort of break out board for the ATMega328. It’s compatible with the Arduino IDE and also contains a USB port for easy programming. The Trinket is hooked up to a GY-521 accelerometer, which allows it to detect motion. When the Trinket senses that the device has been moved, it emits a loud high-pitched whine from a piezo speaker.

To arm the device, the user first holds the power button for 3 seconds. Then the user has ten seconds to enter their secret code. This ensures that the device is never armed accidentally and that the user always remembers the code before arming the device. The code is entered via four push buttons mounted to a PCB. The code and code length can both be easily modified in the Trinket software.

Once the code is entered, the status LED will turn solid. This indicates to the user that the device must be placed stationary. The LED will turn off after 20 seconds, indicating that the alarm is now armed. If the bag is moved for more than five seconds at a time, the alarm will sound. The slight delay gives the user just enough time to disarm the alarm. This parameter can also be easily configured via software.

23 thoughts on “Motion Activated Alarm For Your Bag

    1. Nah, to obvious. With all the shoe and pressure cooker bomb scares, you could walk in with 6 brick-red tubes and an alarmclock around your neck. Just don’t carry to many pens…

      1. Better yet, attach a small audio device and a decent (non 3d printed) speak and 30 seconds after the theft, let it loop a sample that screems “Allah u ackbar..” very loudly.

  1. Wouldn’t this serve to alert a brave thief that the bag really does contain something of value, and they take a chance and run away with it fast as they can? I don’t know if one is going to carry around valuable stuff to that degree, they should get comfortable carrying a bag around as women are. Other than my wallet and checkbook, the only thing of value I carry is my phone that fits in my pocket.

  2. How often does anyone even look up when they hear a car alarm go off? Seems like you’d still need to be within hearing range of the alarm, since you would be the only one that cares. Plus, a quick smack with a rock/book/foot would end the alarm. Nice UI (especially the need code to activate), but doubtful it would be much of a deterrent. Like pretty much all theft, the best defense is really really good insurance (and the documentation to go with it).

    1. Friends of mine have had bags stolen from under tables *while they’ve been sat there*, in that case this would be ideal. Sure if you’re leaving your bag out of ear or eyeshot then that’s a different issue, but I wouldn’t be doing that, this is for those quick trips to the bar. Excellent project!

      1. That is an excellent solution NiN!

        All you need to do is attach a solar strip that will ensure the battery gets charged so that the GPS does not lose out power.

        It is has a very small footprint as well. Just needs to be disguised appropriately.

  3. So the burglar has 5 seconds to open the bag and squash the alarm before it has a chance to make a sound? Or he could simply throw it far away to create a diversion and walk calmly away in another direction,,, Interesting concept! :-)

  4. I made something like this when I was at school in the early1980s. Though that was just a mercury switch to detect motion, a 555 monostable to give arming time, and a simple transistor to switch and latch a buzzer.

      1. Popular project I guess. I did something similar with a mercury switch salvaged from a junked alarm system feeding the gate of an SCR and a hidden 2.5mm jack to disarm when a dummy plug was inserted (SCR source->jack ring->jack presence detect->buzzer).

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