Hackable/DIY wireless home security sensor solutions

I want to replace my old security system with something more modern, and preferrably something that does not mandate monthly fees and/or proprietary hardware/communication protocols. My old system has wireless sensors, but it uses traditional FM signaling which most computers/phones are unable to intercept (yeah, I dream of a phone with a good programmable software radio). An ideal solution would be Bluetooth LE sensors (door, motion, sirens etc) which I could monitor from an aged Android GSM phone (I can write the software myself if I have to). This "alarm central phone" would then be able to signal alerts to an app and/or SMS messages to other phones (the ones we carry). Any pointers?