What a deadlock actually does
A deadbolt throws a solid metal bolt into the door frame and cannot be pushed back with a card or a shim like a spring latch can. That single property is why a deadlock is the highest-value upgrade on most front doors.
Its effectiveness depends heavily on what it throws into. A strong bolt in a soft pine jamb with 20mm screws is not a strong door.
Single cylinder
Key on the outside, a thumb turn on the inside. You can always get out without a key.
- Best for doors with no glass panel nearby.
- Safest option for fire egress, especially with children or older occupants.
- Faster to exit in a hurry, which matters more than most people expect.
Double cylinder
Key on both sides. It stops an intruder reaching through broken glass or a pet door to turn the bolt, but it also means you cannot leave without the key.
- Consider it only where glass is within arm's reach of the lock.
- If fitted, keep a key on a hook near the door — but out of sight from the glass.
- Not appropriate on a primary escape route in many households; weigh this carefully.
The parts nobody looks at
Two cheap details do more for security than an expensive cylinder: a reinforced strike plate and long screws that reach the structural stud behind the jamb.
- Reinforced strike plate rather than the thin pressed one supplied in the box.
- Screws of at least 65mm into the framing, not just the door jamb.
- Bolt throw of 25mm or more where the door allows it.
- Hinge-side bolts on outward-opening doors.
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