Odd syncopation by by chained, because formerly bars were closed with a string. It is a safety mechanism that locks two or more parts with a key or combination to open it.
It is a portable security device. It consists of a metal box and a removable metal ring, which through the use of a key opens and closes according to the need. Safe.
Lock: Lock loose contained in a box of metal by means of Eyebolts ensures doors, windows, lids of chests, suitcases, etc.
Prison slang " padlock " meaning a jailer, guard or celador (Argentina )