Good stuff. If you really want to make it as breach proof as possible, think about connecting it to an independent battery - it can periodically be charged - this way if someone tries to break in by cutting off your battery connection, the device would still work.
Ask talhawaleed to guide you as he has experience with this product and he's got good technical know-how - I know from his thread on maintaining UPS/Car batteries - maybe you can do the install yourself.
Good luck and do let us know how it turns out for you.