Rekey or replace your locks: which do you need?

What does rekeying a lock actually do?

Rekeying changes which key turns the lock without changing the lock itself. The old keys stop working and you get new ones.

Most house locks in the US are pin tumbler locks. Inside the round part you put the key into (the cylinder) is a plug that turns. Small stacks of pins sit across the gap between the plug and the housing around it. Each stack has a bottom pin, a top pin and a spring. When there is no key, the top pins sit across that gap and stop the plug from turning.

The cuts on a key lift each stack to a precise height, so the gap between bottom and top pin lines up with the edge of the plug. That edge is called the shear line. With every stack lined up, the plug turns.

To rekey, the locksmith takes the plug out and swaps the bottom pins for ones that match a new key. The lock body, the handle, the deadbolt and the finish stay exactly as they were. Only the key changes.

When is rekeying enough?

When the locks turn smoothly, latch firmly and are a type you are happy with. The goal then is only control over who has a key.

• You bought or moved into a home and don't know who holds old keys.
• A key was lost or stolen, or a roommate, partner or tenant moved out.
• A contractor, cleaner or dog walker had a key and no longer needs one.
• You carry three different keys for three doors and want one.

Rekeying keeps the parts you already paid for, so it is usually the cheaper and quicker choice when the hardware is sound. Our new home lock checklist covers the move-in case in detail.

When should you replace the lock instead?

Replace when the lock itself is the problem: it is broken, worn, weak, or not the lock you want. A rekey can't fix any of those.

• It is damaged. A cylinder that was drilled, pried or forced, a bent bolt, a cracked housing.
• It is worn out. Keys that need jiggling, a knob that wobbles, a bolt that won't fully extend. Sometimes a repair fixes it; see lock repair.
• It is low grade. Some bargain locks use thin parts that bend or wear quickly. A better grade is a real upgrade on a door you use every day.
• You want a different kind of lock. A keypad, a smart lock, a deadbolt where there was only a knob, or a different finish to match new doors.
• The keyways don't match. If you want one key for the whole house and one lock is a brand that can't take that key, replacing that one lock is often simpler.

How do rekeying and replacing compare?

The short version: a rekey changes the key, a replacement changes the lock. The table shows what each one does and does not change.

What do lock grades mean?

The Builders Hardware Manufacturers Association (BHMA) grades many locks 1, 2 or 3, with grade 1 the highest. The grade reflects how a lock performs in standard tests.

BHMA says the grades are defined by rising levels of performance in each ANSI/BHMA standard, and that a product's grade can also be found from its BHMA product number (BHMA product grade levels). For home locks, BHMA also runs a consumer site that rates residential hardware for security, durability and finish (Secure Home).

What that means in practice:

• Look for the grade or rating on the box or the maker's product page. If a lock has no grade listed anywhere, ask why.
• Front and back doors get the most use and the most attention from anyone trying to get in. Spend there first.
• A strong lock on a weak frame still fails at the frame. Long screws in the strike plate and a solid door matter as much as the grade.

Can all your locks work with one key?

Usually yes, if the locks share a keyway, which is the shape of the key slot. Locks of the same brand family usually do; mixing brands is where it gets harder.

Two common keyways in US homes belong to Kwikset and Schlage, and their keys don't fit each other's locks. A house with a Kwikset front door and a Schlage back door can't share one key by rekeying alone. The fix is to replace the odd lock, or its cylinder, with one that takes the keyway you want.

Making locks work with the same key is called keying them alike. Tell the locksmith how many locks you have and the brand on each before the visit. That decides whether it is a simple rekey or a rekey plus one new lock.

What about locks you can rekey yourself?

Some locks are built so the owner can rekey them with a small tool, as long as there is a working key. Kwikset's SmartKey is the best-known example.

Kwikset describes SmartKey as re-key technology that lets you re-key the lock yourself, using your current working key, the SmartKey tool and a new key, after which the old key no longer works (Kwikset SmartKey).

That is handy, with limits:

• You need a working key for each lock. If the previous owner left none, or the key is lost, you can't use the owner process.
• You can only set the lock to a key you already have, so you still need new keys cut.
• It does not fix a worn or damaged lock.
• Locks from other brands in the house still need their own rekey or replacement.

Does a master key system change the answer?

Yes. A master keyed lock has extra parts inside so that two different keys open it, and those parts change how it should be rekeyed.

Master keying is common in rentals, offices and some new buildings. If you own a home or a unit that was once part of a master key system, a standard rekey should remove the extra parts so only your key works. Ask the locksmith to check for them.

If you manage several units and want a master key on purpose, plan it rather than adding it one lock at a time. Our key control guide for landlords and the master key systems page explain how that is set up.

When does it make sense to do both?

Often. Replace the one lock that is worn or weak, and rekey all the others to the same new key.

A typical example: the front door deadbolt sticks and the back door has no deadbolt at all. The front deadbolt is replaced, a deadbolt is added at the back, and the garage entry lock is rekeyed. Everything ends up on one key. That keeps the cost of new hardware to the doors that need it.

What should you tell the locksmith before the visit?

How many locks, which brands, which ones stick, and whether you want one key for all. With that, the locksmith can give you a total before driving out.

• Count every keyed lock: knobs, levers and deadbolts on each outside door, plus the door from the garage.
• Read the brand on the lock face or the inside of the door.
• Note any lock that is stiff, loose or hard to lock.
• Say whether you have a working key for each lock.
• Say how many new keys you want.

When you get the quote, check whether it is a total for the whole visit or a price per lock plus a trip fee. Either is fine as long as you know the full amount before anyone drives out. See rekey service or lock change if you are in the Memphis area.