A deadbolt is a locking mechanism that does not have a spring latch. The deadbolt can only be opened by manually turning the key or by rotating the turn piece. Because there is no spring mechanism added security is provided. Deadbolts are often used in association with a keyed knob or lever for the additional security they achieve.
A Deadbolt that locks by key on the outside and a turn piece on the inside of the door.
A Deadbolt that locks by key on the outside and inside of the door. **Double Cylinder locks on doors used for exiting a building or a home are a life safety hazard in times of emergency and are not recommended**
A one sided deadbolt locks a door from the inside. These are commonly used on patio doors.