Raspberry Pi to passively monitor alarm panel?

I’ve been pondering retrofitting ST to my parents’ house. They (a) don’t want to see a bunch of new sensors everywhere, and (b) already have a hardwired alarm system with contact sensors and PIR sensors everywhere. It seems that this could serve as the basis for a nice ST system.

So, I’m considering using a Raspberry Pi with a large number of IO channels to passively monitor each zone/sensor at the tie-in to the alarm panel. The alarm system is active and monitored, and my parents use it regularly – so of paramount importance is not disrupting the operation of the alarm system!

Some questions:

  • Has anybody tried a passive monitoring integration into an alarm system? What signal levels could I expect? Total off-the-wall guess: The sensors in each zone are wired in a series loop any individual sensor can open the loop if tripped. Then, you’d expect a pull-up on one side of the alarm panel and ground on the other side – meaning that the first side would read high when normal and low when tripped. Is there a standard for what voltages these systems run at? It seems that getting a multi-channel A/D board for the Raspberry Pi would be the safest/easiest bet, if possibly also overkill.
  • Should I just write the software on the Raspberry Pi to make HTTPS calls to the ST hub on each observed state change? Is there a better way to do this? I could also use an Arduino with ThingShield to avoid the RPi->ST messiness, but not sure if that’s better.

There are many projects for monitoring existing hardwired systems so they can be somewhat integrated with smart things.

Use the quick browse list in the community created wiki in the project section and look under “security.” :sunglasses:

A lot of people used to do this with the SmartThings thingshield, but unfortunately it has not been available for sale for sometime. Popular alternative which is available is alarm decoder.

If you try to do it yourself be aware that many alarm systems actually have three states for their sensors, not just on and off or open/close. This is why people usually end up adding an additional hardware piece.


ThingShield is back in stock!

Agree with JD, Alarm Decoder makes a product that basically acts as another keypad on the alarm. They even have a complete solution with Pi too:

Or you can try the AD2Pi hooked up to an Arduino with a ST ThingShield:


wish there was an option to integrate the 2Gig / Alarm.com panel into ST… :frowning: