What is a double cylinder deadbolt?

• A. Key on both sides (interior and exterior)
• B. Key only on exterior
• C. Thumb turn on interior
• D. Keypad entry

Answer: (A)

A double cylinder deadbolt requires a key to operate from both sides of the door. In other words, you can’t just turn a thumb latch or knob on the interior to open it; a key must be used on inside and outside to lock or unlock the bolt. This design is often used where there’s a glass panel near the door or potential reach-ins from inside, since it prevents someone from simply turning a lever or thumb-turn from inside if they’ve gained access to the interior. The trade-off is that in an emergency, you must have a key to exit, which can slow egress. So the defining description is a deadbolt that needs a key on both interior and exterior sides.