A spring latch in a knob can sometimes be slipped or forced. A deadbolt throws a solid bolt into the frame that doesn't retract unless the key or thumbturn moves it.
Single vs. double cylinder
A single-cylinder deadbolt has a key outside and a thumbturn inside, which is the usual choice for homes because you can get out quickly in an emergency. A double-cylinder deadbolt needs a key on both sides. Check local fire and building codes before fitting one on a door used as an exit.
Grades
ANSI/BHMA grades rate durability and strength. Grade 1 is the heaviest-duty, Grade 2 is common for residential exterior doors, and Grade 3 is entry level. For a front door, Grade 1 or 2 is a reasonable target.
Installation details that matter
- Use a reinforced strike plate with long screws that reach the wall stud
- Make sure the bolt fully extends; it should throw at least an inch
- Check the door is aligned so the bolt doesn't bind
Getting one fitted
A locksmith can add a deadbolt to a door that doesn't have one; the price list shows new lock installation on a door without a lock hole starting at $85. See residential services.
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