A lock, often known as a door, is a tile in Chip's Challenge that remains acting wall as long as Chip does not have a key of the same color; if Chip has a key of the same color, the lock will then be acting dirt. With the exception of green keys, a lock will use up the key that opened it.
Locks come in four colors:
A lock on top of a clone machine will refuse to open even if Chip has the required key, as with all other tiles on top of a clone machine. If a block is on top of a lock (or any other Chip-removable tile) and Chip pushes on the block without the correct key, the block is flicked just as with any other Chip-acting wall under it. If the key is in Chip's possession, the block is pushed just as if it were a normal block with nothing underneath it.
An interesting behavior is when a transparent tile is located on top of a lock. While Chip cannot step on it without the proper key, stepping on the lock itself does not use the key. In the case when Chip is killed from stepping on a monster in this manner, the lock will disappear although the key was never used. (Since a lock is not transparent, the Transparency Glitch does not occur here.) However, Chip is unable to step on another Chip on top of a lock, just as if it was a normal non-moving Chip tile.