MIMOLITE - monitor voltage

I wish to use the MIMOLITE to alert me if my security system alarms. I thought the best way to do this is to monitor the 12volt siren circuit.

I’m having difficulties getting this to work. It seems the voltage doesn’t do a refresh unless I manually issue a ON/Off command. When I issue the command the voltage indicator changes and I get the desired alert. If I don’t use the manual on/off command the voltage read stays the same even when I plug/unplug the power to the INPUT terminals.

I’m using Smartthings and I can get an alert when I I select the ON/Off button but not when I plug/unplug the power to the input terminals.

Any suggestions would be greatly appreciated.