How to choose a deadbolt

The grades, and what they were measured on

The American National Standards Institute and the Builders Hardware Manufacturers Association grade locks on measured tests rather than marketing.

Grade 3 is basic residential. It survives two strikes in the hammer test and a hundred thousand operating cycles. This is what most homes ship with.

Grade 2 is heavy residential or light commercial. Five strikes, a hundred and fifty thousand cycles.

Grade 1 is commercial and the highest. Ten strikes, two hundred and fifty thousand cycles.

So Grade 1 takes five times the impact of Grade 3 and lasts two and a half times as long in normal use. On a front door that difference costs perhaps fifty dollars.

Look for the grade printed on the packaging. If a lock does not state one, it has not been graded, and untested is not the same as good.

Throw, and why an inch is the number

The throw is how far the bolt extends out of the door when locked. Extend the bolt and measure from the face of the door.

One inch is the standard for a reason. A shorter bolt does not reach far enough past the frame surface into the structure behind it, so the amount of material resisting a kick is small.

Many cheap deadbolts and most latch bolts throw considerably less. A spring latch typically throws about half an inch and is not a security device at all, which is why a deadbolt exists as a separate lock in the first place.

Check the fit too. The bolt should extend fully with no resistance when the door is closed. If it needs the door pulled or lifted to lock, the strike is misaligned and the bolt is only partly engaging, which quietly undoes everything else.

The strike plate is the real answer

This is the part that changes outcomes.

A standard strike plate is a thin piece of metal held by two three quarter inch screws. Those screws reach into the door jamb, which is a decorative board nailed to the framing. When somebody kicks the door, the bolt does not break and the lock does not fail. The jamb splits along the grain and the whole strike tears out.

A reinforced strike box is a heavier plate with a metal cup behind it, held by four three inch screws that pass through the jamb and bite into the structural stud. Now the force has to break the house rather than a board.

The parts cost around ten to twenty dollars. Fitting takes minutes. It is the highest return security upgrade available on a residential door and almost nobody does it.

Do the hinges as well. Replace two screws in each hinge with three inch screws into the stud. Hinges fail in a kick as often as strikes do.

Single cylinder or double cylinder

A single cylinder deadbolt takes a key outside and a thumbturn inside. A double cylinder takes a key on both sides.

People with glass beside the door often want a double cylinder, so that breaking the glass and reaching through does not let somebody turn the thumbturn.

The trade is escape. In a fire, in smoke, in the dark, with children, a double cylinder needs a key to get out. People have died behind them. Many jurisdictions restrict them on residential exits and building codes should be checked before fitting one.

There are better answers to glass beside a door. Security film on the glazing, replacing the panel with laminated glass, or a thumbturn that can be locked with a key when the house is empty and left free while it is occupied.

If you fit a double cylinder anyway, keep a key on a hook within reach of the door, out of arm's reach of the glass, and make sure everybody in the house knows where it is.

Things that matter more than the brand

Fit the deadbolt at a sensible height, several inches above the handle set, so that a single kick cannot load both locks in the same place.

Check the door itself. A hollow core door fitted as an exterior door has a cardboard honeycomb around the lock and will fail there no matter what you fit. Tap it. A hollow core sounds like a drum.

Check the gap between door and frame. More than an eighth of an inch gives room for a pry bar and sometimes for a shim past the latch.

On an outward opening door, fit hinges with non removable pins or a security stud, because otherwise the hinge side comes apart with a screwdriver.

And consider key control. A common keyway means the key can be copied at any hardware store. If that matters to you, ask about a restricted keyway rather than trusting a do not duplicate stamp, which has no legal force and stops nobody.