I've just finished a project doing exactly this with a galaxy 504. Thanks very much for your input (no pun intended) I don't want to damage the rio or arduino! With the aforementioned pull-up links of the rio removed, could I safely connect the outputs directly to the arduino digital input pins using the INPUT_PULLUP feature (to clarify digitalWrite(pin, HIGH)

I believe this means they are open collectors when the links are removed? They can apply a +12V signal, if required, by fitting the appropriate pull-up jumper supplied.' Without the jumper links (LK1-4) fitted, the outputs will float in 'The 4 outputs are switched 0V (0V active). I've lifted the following statement from the installation manual (which can be found in various places although this link works: ): I plan to power the Arduino using a DC-DC 12v->5V module (this has tolerance that would support an output voltage of 13.8v which seems common for the 12v outputs of the honeywell alarm system).

I'm going to be using a rio (remote input output) device manufactured by Honeywell to get the outputs from the alarm system. I'm looking to interface with a honeywell galaxy alarm system (g3-96)

Honeywell galaxy alarm