tack:
I'm thinking some kind of saloon or revolving door. Ideally I need to restrict to single entries to track people in and out: my perfect solution would be an RFID detector doorway that just scans everyone, but it seems that kind of range isn't easily (or inexpensively) achieved.
Instead of locking a door why not rig-up a custom optical turnstile?
Edit: What I mean is have multiple optical/IR sensors arranged horizontally a half inch or so apart, about midway up your doorway/passage-way, that trigger when something goes past them. You'd need at least two, but three or four could make it less error prone. You wouldn't even need a barrier because the sequence of the sensors being triggered indicates if someone is entering or exiting. For example if you three sensors labeled 1, 2, 3; triggering the sensors in increasing order would happen for movement in one direction, sensors triggering in decreasing order would mean movement in the other.