Some rarer types are either upright like school lockers (which requires the bicycle to be suspended from a hook inside) or are stacked twice high, with some attendant difficulties in inserting and removing bikes in the top row.
However, problems encountered with this approach (such as being used by homeless people as sleepouts, or for the storage of things other than bicycles) have led to newer designs which incorporate windows or grilles through which inspection staff can see inside.
Bike locker locks depend on whether the boxes are rented out on a fixed period basis, or whether they are first-come-first served.
Those which are usable on a more casual basis either allow the door to be locked by a padlock brought along by the user, or provide a rental system that dispenses a key or code.
The system was pioneered by Bicycle Tree International, headquartered in Geneva, Switzerland, a company which has however since ceased operations.