Few locksmith terms cause more confusion — or more overspending — than these two. Rekeying and replacing both end with your old key useless and a new key in your hand. The difference is what happens in between, what it costs, and when each one is the right answer.
What rekeying actually is
Inside every keyed cylinder sit spring-loaded pins cut to match one specific key's depths. Rekeying means a locksmith opens that cylinder, discards the old pins, and fits new pins matched to a new key. The lock on your door — the bolt, the housing, the finish — stays exactly as it is. Only the key changes. The job takes minutes per lock, the hardware cost is zero, and it completely answers the question "who else can open my door?" as long as the lock itself is sound. It is the default service after moving in, a tenant change, a breakup, or a lost key.
What changing a lock adds
Replacing the lock swaps the hardware itself. That buys you things rekeying cannot: a higher security grade and stronger bolt; a different style or finish; a keypad or smart lock instead of a keyed one; and escape from hardware that is worn, rusted, builder-cheap, or a brand whose parts are disappearing. It also costs more — hardware plus labor — and on a whole house the difference multiplies by every exterior door.
The decision, door by door
Rekey when the lock is quality hardware, works smoothly, and your only problem is key control. Replace when the key sticks or the cylinder feels gritty (wear lives in the parts rekeying keeps), when the lock is a no-name builder unit, when you want keyless entry, or when the door deserves a better grade of protection. Mixed verdicts are normal: we regularly rekey three doors and replace one. Anyone quoting you an all-or-nothing answer for a whole house without looking at the locks is selling, not advising. Our residential locksmith page describes how we assess each door.
What about security — is a rekeyed lock weaker?
No. A rekeyed lock is exactly as secure as it was the day it was installed with that new key combination — the pins are new, the old key is dead, and the bolt and housing never changed. Security upgrades come from better hardware, which is a replacement conversation (see deadbolt grades), not from rekeying itself. One more option worth knowing: restricted keyways. Rekeying into a restricted system means future copies require your authorization — kiosk copies become impossible. For rentals and homes with frequent helper turnover, that single upgrade ends the "copies floating around" problem permanently.
Timing and cost expectations
A typical home's exterior locks can be rekeyed in under an hour; full replacement runs longer and scales with door count and hardware choice. Either job should come with per-door pricing agreed before work starts, new keys tested in every lock in front of you, and — if you want it — all exterior doors keyed alike so one key runs the house. However the math lands for your doors, make the call in the first week of a move or the first day after a key goes missing; the service is cheap, the exposure is not.
The same decision, for landlords and businesses
Everything above applies double when the property is not yours to live in. Landlords rekey between tenancies because the liability question — "who could enter this unit?" — must have a documented answer; keeping the rekey invoices is part of the answer. Businesses face the version with more doors: a single departure rarely justifies new hardware everywhere, but it justifies a rekey of every cylinder that person's key opened, which is exactly the scenario master key planning exists to make cheap. And in both worlds, restricted keyways are the upgrade that changes the future: once copies require authorization, rekeying becomes an occasional event instead of a recurring anxiety.