A bump key is easily hidden among other keys on a keyring; it's just a key cut to the lowest depths in all positions, otherwise it looks just like any other key

A bump key is easily hidden among other keys on a keyring; it's just a key cut to the lowest depths in all positions, otherwise it looks just like any other key. It's a lot less obvious than a set of lock picks. Bump keys, as others have posted, are very crude and rough on the internals of a lock so I'd say use them sparingly, and never without the lock owner's explicit permission of course. But they do have a place. (And require practice too!)