I needed to figure out a way to secure my safe in my dorm. We can't bolt or screw things into the floor or the walls of my room, so I opted for a cable lock. But of course, that isn't the most secure way of tying down a safe. I remember seeing a Sonic Shock Alarm in one of the classrooms and though to myself, "that would work great!" Unfortunately, it's priced at around $100 online. Too much for a student who just broke the bank.
That's when my DIY brain kicked into gear and I started to design my own electronic tether alarm, catered to my own needs of course.
My ideas strangely lead me to another 'able: 15 minutes SMS door entry alarm by PanadoL. Through his 'able, I discovered that some magnetic window alarms have switches that are normally open. In other words, when the switch is open, the alarm turns on. I realized that if I replaced the reed switch in the alarm for a wire, it would act like an electronic tether alarm. (like the Sonic Shock Alarm) Because my alarm is going to be secured inside of my safe, I don't need to have a locked metal box to secure the alarm.
I based my alarm around a GE Magnetic Window Alarm that I picked up at my local home improvement store. Lucky for me, it was one of the alarms with a normally open reed switch. I replaced the reed switch with a 2 screw terminal block so I could quickly attach my electronic tether. (I couldn't opt for a plug of any kind because I was restricted by 1/4" mounting holes that the wire is going to go through)
For many reasons, I also replaced the 4 - 1.5v LR44G button cell batteries that it had with 4 AA batteries. First of all, AA batteries are extremely easier to get. Secondly, AA batteries have a starting voltage of around 1.6v (on average) vs the 1.5v of button cells. Therefore, this already loud alarm will get (initially) an extra 0.4v boost! The final reason is because AA batteries will last a lot longer than button cell batteries. Therefore, if someone does make away with my safe with the alarm blaring, the alarm will go strong for hours. I’ve yet to test exactly how long though. Not eager about hearing that alarm go off for hours.
For my security tether, I will probably use a standard 4 wire telephone plug. However, I will only connect one of the 4 wires for the alarm, and use the rest of them as decoy.
I will upload a photo of the completed set up soon. Sorry if it is confusing without it.
Please leave any comments, questions, or concerns you may have. Be nice because this is my first submission to Instructables!