In addition to surveillance, you will want an access control system - keypads that tenants are required to use for both coming onto the property and leaving. Most vendors in this industry offer access control with software that compiles an activity log so that you know when Customer X arrived and also when that person left.

Taken one step further, your access and video systems can be synchronized with some companies so that whenever someone punches in a code, that 'event' is time-stamped on your video system. This way, you can search video by access code, by unit number, camera position and, of course, by day/time.