I've got AVP 1&2 so I'll look this weekend...
I'm confused on one bit though...Who is using the detector? Is the player using it to detect enemy, or the other way around?
if the player is using it you would just need one trigger setpos'd every time the ap sensor 'sweeps" (nominally around 1.5 seconds or so) and setpos'd to [0,0,0] between sweeps. Set it up to detect anyone's presence and filter out the player himself and or friendlies and already tracked targets. I am working on something very similar to this right now, so perhaps we could share some ideas...I will post something soon so you can check it out.
If the enemy is using it, I would suggest limiting it's use to the group leader, thus cutting down a lot of unecessary triggers, but using the same technique above...
an alternate method would be to use a function like improvednearestobj.sqs or something like that in lieu of a trigger.
-Grendel