I’ve been a fairly happy customer for a few years but I will be moving in February and I’m torn on what the best system is for me. The home in question has a ADT system in place that has existing sensors. For that reason I would suspect that the best option is the GC3. I like the BLE and Z-Wave + on the Qolsys but the lack of Honeywell support seems like an unnecessary investment in new sensors. Anything I’m missing?
Note that ADT like Alarm.com is sold through a network of dealers and doesn’t have just one panel type. Dealers use a variety of systems, so you would want to verify the model of alarm panel that is there, or the model of the wireless sensors.
If Honeywell, yep the GC3 would work out of the box. If you are interested in Qolsys, note that a translator could be used to employ existing sensors and translate them into GE wireless signals for the Qolsys panel.