What we have used in the past is very crude by current standards.
We are planning upon getting a DVR unit with motion-detection cameras, they can film numerous screens simultaneously and then you can enlarge the picture that interests you later. The motion switched camera saves alot of empty recording too.
We currently have 100's of tapes full of past tours and do you think we ever have the time to watch them? No!
I guess some DVR units can record several weeks of action at a time?
Ghost-Hunters who were here a couple of times had such a unit.