Recently there were a bunch of videos going around the net about some of the greatest pickpockets in the world. Simply put, if they wanted something you had, they were going to take it and you probably wouldn’t notice. I’ve always kept my wallet in my front pocket, and usually with my hand on it, but they even showed them getting around that in the video (you can’t always be vigilant).
I had the idea to make some kind of alarm that would go off if anyone but me removed the wallet from my pocket. A quick google search revealed tons of wallet alarms, but I noticed that they all had a credit card form factor(that’s good) and would make noise when exposed to light(that’s bad). This represents a problem since the pickpockets in the videos tended not to open the wallets till later at another location. I needed something that would make noise as it was removed from my pocket. Most importantly, I needed the alarm to be located inside the wallet. This immediately makes the wallet undesirable and will hopefully make someone drop it like hot coals.
I happened to have a few little magnetic window alarms sitting around. They’re just a loud buzzer with a magnetic reed switch. After holding one up to my poor fat old neglected wallet, I saw that the alarm was roughly the same thickness as all the old business cards I should’ve cleaned out of my wallet anyway.
I promptly tore the alarm apart and started planning how I was going to slim it down as much as possible. Most of the thickness is from the case, the batteries would be the next biggest contributor. After destroying the buzzer from one by trying to pry it from its plastic enclosure, I decided to leave the buzzer and simply live with the thickness. After all, if the prototype worked well, I could design something in a credit card form factor later. That is, if my attention span were long enough to do a thing like that.
The only real modification I made to the alarm itself was to un solder the reed switch and relocate it to the very end of the whole mess. This would allow it to be at the “spine” of the wallet and keep the power switch at the opening for easy access. The rest was simply cutting away as much bulk as possible and hot gluing things together.
It actually works exactly as expected. There are two choices for the alarm, a single chime when removed, or a constant alarm. The only big upgrade that I would suggest would be a stronger magnet so it wouldn’t need to be aligned perfectly.