A deadbolt provides much better protection against forced entry than a knob lock. On an exterior door, though, the real answer is to have both: the knob or lever latches the door for everyday use, and the deadbolt does the security work. Here is why the two locks behave so differently and what to look for when choosing a deadbolt.
Questions about the locks on your own doors? Call (613) 707-4884.
How a Knob Lock Works
A knob lock, or a lever lock, uses a spring latch, the angled tongue that clicks into the frame when the door swings shut. It's convenient, because the door locks as you close it. But the latch is spring-loaded and fairly short, so it can be pushed back. Its weak points:
- The angled latch can sometimes be forced or slipped back, especially if the door fits loosely in the frame.
- The lock cylinder sits inside the knob, which can be attacked by force.
- The short latch gives little resistance to a kicked door.
Many knob locks include a small "deadlatch" pin that helps resist slipping, but they still aren't designed to stop a forced entry.
How a Deadbolt Works
A deadbolt's bolt is not spring-loaded. It only moves when you turn the key or thumb-turn, and once extended it can't be pushed back by pressure on the bolt. It is square-ended and projects further into the frame than a spring latch. So a deadbolt:
- can't be slipped like a spring latch;
- spreads the force of a kick into the strike plate and the frame;
- keeps the lock cylinder in a separate, sturdier housing.
Side-by-Side
- Locks automatically when the door closes: knob lock yes; deadbolt no (unless it is a motorized smart deadbolt with auto-lock).
- Resists slipping the latch: knob lock limited; deadbolt yes.
- Resists a kicked door: knob lock poor; deadbolt good, if the strike and frame are solid.
- Best use: knob lock for interior doors and everyday latching; deadbolt for the security of every exterior door.
What Makes a Good Deadbolt
Grade
Door hardware is graded under ANSI/BHMA standards. Grade 1 is the highest level of performance, Grade 2 is intermediate and Grade 3 is basic. For example, the BHMA standard for bored locks requires 1,000,000 test cycles for Grade 1, 400,000 for Grade 2 and 200,000 for Grade 3. For an exterior door, choose at least a Grade 2 deadbolt, or Grade 1 for heavy use or higher risk.
Strike plate and screws
A deadbolt is only as strong as what it locks into. A reinforced strike plate fastened with long screws that reach the wall framing makes a bigger difference than most people expect.
Single or double cylinder
A single-cylinder deadbolt has a key outside and a thumb-turn inside. A double-cylinder model needs a key on both sides. That can help beside a glass panel, but it can slow your escape in a fire or emergency if the key isn't at hand. For most homes, a single-cylinder deadbolt is the practical choice.
Key control
When you install new deadbolts, consider having them keyed to the same key as your other exterior locks. Our article on keyed-alike locks explains how that works.
The Bottom Line
Keep the knob or lever for convenience, and add a properly installed deadbolt to every exterior door, including the door from the garage into the house. If your doors only have knob locks, our deadbolt installation service can add one. Call (613) 707-4884.