You don't know who else has a key
When you buy or rent a home, the keys you are handed are only some of the keys that exist. Previous owners, tenants, cleaners, dog walkers, contractors, neighbours who watered the plants and real estate agents may all have had copies. Even when a seller says they collected every key, nobody can promise that.
Rekeying changes the pins inside the cylinder so a new key works and every old one stops. The hardware stays on the door.
What rekeying involves
The locksmith removes the cylinder, takes out the old pins, fits a new set to match a new key and puts the lock back. It takes a few minutes per lock. Several locks can be rekeyed to the same key at the same time, so one key opens the front door, the side door and the garage, as long as the locks share a keyway.
Rekey or replace?
Rekey when the locks work well and you like them. Replace when they are worn, damaged, corroded by salt air, or when you want a different kind of lock, such as a keypad deadbolt or a higher-security cylinder. Many people do both: rekey the good locks and replace the one that has always stuck.
Renters
Renters can ask the landlord to rekey before move-in. Some landlords do this between every tenant as a matter of course; others agree if the tenant pays. Get permission in writing before changing anything, and give the landlord a copy of the new key if the lease requires it.
After renovations
Builders, painters and other trades often get a key or a lockbox code during a renovation. When the work ends, rekeying is a simple way to close that chapter, and resetting any keypad codes is the electronic equivalent.
What it costs
On the current price list, residential and commercial rekeys start at $19.00 on top of the $29.00 service call fee, plus labour. There is also a 20% coupon with any rekey. The locksmith confirms the total before starting.
