whats the frequency on the FOBs for the alarm/access?
If they have a decent smart phone or iphone...
install and run the apps for bluetooth signal monitoring (one I used to use on my old mio windows CE phone would permit me to setup for passive only, I cant find a modern version that has the same list on the can) and it would record all the activity until the phones battery went flat OR the memory card went full.
run that and it should give you the timings for any activity thats happening, including when things that are being active go inactive.

