Hardwiring Siren to ADT Smartthings Panel?

Has anyone looked into hardwiring anything on the back of their ADT Smartthings Panel? It’s clearly not designed for this, but probing around on the back of the circuit board it looks like there are a few inputs and outputs that could be utilized with a little bit of soldering work.

I was specifically looking to integrate a second siren to the panel since the built-in one is too quiet, and I’m replacing a panel that already had an auxilliary siren installed. I realize I can do a z-wave or zigbee siren, but it would be nice to have a siren that is not dependent on the cloud, just like the built-in siren.

I noticed there was bell + and bell - on the back, but I’m measuring 13.5VDC when there is no alarm active, and 14.0VDC when the siren is active. However I haven’t played around enough to know whether the 13.5VDC is ghost voltage and would disappear when a minimal load is applied.

Before I spend too much time on this, I’d like to know if anyone has looked into this.

I did also notice that the zone 1 and zone 2 have 5VDC relative to COM, so it’s possible that they might be useful with hardwired sensors. But I haven’t looked further on those either.

Hi, I bought ADT Smartthings last month and I am in the same situation; looking for additional siren and would like to do not cloud dependent.
Did you get any conclusion about bell+ and bell- ?

I´ve used a 7805 volt regulator conected to Bel + & Bel- to control a 5 volt relay. Then, you can control whatever you want with the relay output.

We’re you measuring the same voltage that I was? 13.5V when the siren is off, and 14V when siren is on?

Hi dear meakanek,
Yes the same voltage with no load on it, bur if you add some load (just a resistence to test) then the voltage become almost 0 when siren is off.