Alert when only one pool member left.

I've been tasked with coming up with an alert when there's only one pool member left in the pool. I'm trying to think of the simplest way to go about it. I have created a custom trap using the /config/user_alert.conf before so I'm not worried about that. I'm just trying to think of the easiest way to get the log entry written so the trap will trigger. I tried playing with Priority Group Activation and manually disabling and forcing members offline, but no log entry was written. I've never written an EAV monitor before, would that work? Can anyone think of anything else?