I’m pretty sure most large storage operations (U-Haul, extra space, etc) have per unit door sensors which work in concert with customer check in/out to verify authorized openings.
I can speak for U-Haul specifically because I have used them and a customer can see the sensors in their unit. The sensors are deactivated when a customer checks in.
https://s3-media0.fl.yelpcdn.com/bphoto/K_IeKTxlLTzLBd4F9Ett...
If I don't sign in, as soon as I try to roll my door up the alarms are going to go off. If I don't sign out after closing the door and leaving, the next time I try to sign in I will be denied entry until I speak to a manager and be yelled at about signing out when I leave.