A deadlock is a type of lock that can only be unlocked with a key when it’s in deadlock mode. Deadlocks can contain 3 or 5 levers, with additional levers increasing security. It can be operated using a key from either side of the door and usually works independently to any door knob/lever handles. A deadbolt
is very similar to a deadlock, but the bolt doesn’t contain levers, and instead of being locked and unlocked via a key, it’s often used in bathrooms where it’s operated via a thumbturn.