Double-cylinder deadbolts are often sold as more secure, and sometimes they are. They also bring a serious safety trade-off. Here is how to choose.
What the difference is
A single-cylinder deadbolt has a keyhole outside and a thumb-turn inside. A double-cylinder deadbolt needs a key on both sides.
When double-cylinder is used
Mostly on doors with glass or side windows within reach of the lock. Without the inside key, a person who breaks the glass cannot reach in and turn a thumb-turn.
The safety issue
In a fire, the inside key may not be in the lock, or may not be found in smoke. People can be trapped. Many building and fire codes restrict or prohibit double-cylinder locks on exit doors in homes and buildings. Check the rules that apply to your property before installing one.
Safer alternatives
- Use a single-cylinder deadbolt, with a solid door and no glass close to the lock.
- Fit a security film on side windows.
- Move the deadbolt out of easy reach of the glass.
Rules of thumb
For most family homes, a single-cylinder deadbolt with a good strike plate is the better choice. For commercial doors, exit hardware is set by code. If you are unsure, ask your local fire department or building official.
Get advice
See our deadbolt installation page. We can look at your door and recommend a lock that is secure and safe to leave in an emergency.
The trade-off explained
A double-cylinder deadbolt needs a key on both sides. It stops someone breaking a nearby window and reaching in to turn a thumb turn, but it also means occupants cannot leave quickly without a key in a fire.
What safer options exist
Consider a single-cylinder deadbolt with laminated or reinforced glass near the door, or a key-operated deadbolt whose key stays in a known place. Building and fire codes may limit where double-cylinder locks are used.
Ask before you decide
Talk to a technician about your door and the glass around it. See our deadbolt installation service and standard vs high-security deadbolts.
Questions about a lock or key problem? Apna Locksmith is a Brampton-based mobile locksmith serving Brampton, Vaughan, Caledon, Etobicoke and Halton Hills. Call (289) 406-1500 or see our service areas.