Jeff Sandberg Turns to Software-Defined Radio to Get a '90s Alarm System Talking to Home Assistant

Software engineer Jeff Sandberg has created a considerable upgrade for his '90s-era burglar alarm by integrating it with a Home Assistant-based home automation setup — spying on its wireless signals with a software-defined radio to avoid any hardware modifications.

"My house was built in the mid-90s, when home automation meant a mixture of an intercom system, burglar alarm, and maybe some X10 stuff (I didn't find any of that, sadly)," Sandberg explains. "State-of-the-art burglar alarm systems at the time used cheap little radio transmitters, to avoid the need of running wires all over a house.1 These devices typically take the form of a little box next to a door or window, with a reed switch that is triggered by a magnet attached to the door or window. And my house is chock-full of them."

The system in question is a General Electric Interlogix alarm, with battery-powered sensors that transmit to a central alarm box. "Although their immediate function is readily clear to most people who would care about this sort of thing," Sandberg notes, "how to get the information out of them is somewhat more obscure. Fortunately, smart people on the internet have documented the messages these little boxes put out, and written tools that can decipher them."

Using a Nooelec NESDR, a software-defined radio capable of receiving at the 319.5MHz that the sensors put out, Sandberg used the rtl_433 software tool to listen on the required protocol — capturing each sensor as it's triggered. The software's built-in MQTT support is then used to pass these messages on to an MQTT broker, and from there to Home Assistant. "Reload your Home Assistant config," Sandberg says, "and you're done! You now have your door, window, heat, glass break, and any other sensors you cared to map in Home Assistant."

The full article, which includes a sample YAML configuration for Home Assistant, is available on Sandberg's website.