A single-cylinder deadbolt opens with a key outside and a thumbturn inside — convenient and the right choice for most homes. A double-cylinder deadbolt needs a key on both sides, which helps when there is glass near the door that an intruder could break to reach the thumbturn.
The catch with double cylinders: in an emergency you need the key to get out, so keep one accessible and check local code requirements. Either way, the strike plate and frame matter as much as the lock — a strong deadbolt in a weak frame is theater.
What a good installation includes
Correct backset and bore, a reinforced strike plate with long screws into the framing, and smooth bolt throw without forcing the door. HSI Locksmith installs and replaces deadbolts across South Florida.