Konnected to monitor other Konnected's

I have 4x 6-zone alarm panels and 1x 6-zone add-on board.  I have the add-on board hooked up to a battery backup and would like to use it to monitor the other 4 alarm panels.

In other words, I want to use 4 zones on the battery-backup'd add-on board to know when any of the other 4 boards lose power.  I realize I could solve for this w/ICMP or something like that, but I'm hoping to do it electronically.  I'd like to avoid using any of the 6 zones on the 4 alarm panels to control a relay (they're mostly used up & it would be a pain to rewire).

I was wondering if I could hook the AUX out on these 4 boards to a relay and have that relay open up a circuit when the 12V disappears.  In other words, I'd take zone 1 on the add-on board and loop it through a relay that's powered by the 12V aux on another board.  When that power cuts out, I'd want that loop to open so the battery-powered board could tell me that alarm panel #1 is without power (as if a door/window were open).

I found a bunch of 12V relay modules that expect an input alongside the 12V but I want to use the presence of the 12V alone as the trigger.  On the other side of the relay, I don't want 12V, I just want the circuit opened or closed with whatever voltage the add-on board is passing through (3V I think)  I figure this is doable but not sure what I'm looking for exactly.