The term protector lock has referred to two unrelated lock designs, one invented in the 1850s by Alfred Hobbs, the other in 1874 by Theodor Kromer.
A key from an early example of a Kromer protector lock; these keys were made in all shapes and sizes but the bit is similar in all cases
A lock is a mechanical or electronic fastening device that is released by a physical object, by supplying secret information, by a combination thereof, or it may only be able to be opened from one side, such as a door chain.
A typical modern padlock and its keys
Bronze lock in a form of scorpion from Nalanda, India, 10th century.
Medieval Gothic lock, from the 15th–16th centuries, made of iron, in the Metropolitan Museum of Art (New York City)
Drunk man's lock at the bottom (black lock) and a regular modern lock at the top