 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.Bike Lockers are usually built with solid sides to protect against weather, vandalism, and theft.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.