Usually yes if the keys are stolen, or lost somewhere they could be linked to your address. Usually no if they are almost certainly lost far from home with nothing on them that identifies where you live. When in doubt, change them: the cost of a new cylinder is small next to the risk of a stranger holding a working key.
Losing keys is common, and most lost keys are never found by anyone who could use them. But you cannot know that for certain, so the question is really about how much uncertainty you are prepared to live with.
What should I do first?
Work through the simple checks before paying anyone. Retrace your steps and look where you usually leave keys; keys handed in or spotted outdoors are often left somewhere visible. Ask anyone you live with, and check whether a neighbour, friend or family member holds a spare, which gets you back inside without a locksmith, though it does not settle the security question. 1
If the keys are genuinely gone, it is worth reporting them missing to the police, particularly if anything attached identifies you, and posting in local community groups to see whether they have been found. Never include your address in those posts. 1
When should I definitely change the locks?
Three situations make it close to certain. First, stolen keys: if a bag or coat was taken, treat the keys as in the wrong hands. Second, keys lost together with anything that shows your address, a letter, a driving licence, a delivery label, because a finder can connect key to door. Third, keys lost near your home, where a finder could simply try doors in the street.
In any of these, changing the affected door locks promptly is the sensible course. As the Master Locksmiths Association puts it, changing your locks after losing keys stops anyone without permission from accessing your home. 2 If you rent, tell your landlord or letting agent first; they may arrange the work, and the tenancy agreement may require their involvement. 1
When might I not need to?
If you lost the keys somewhere far from home and nothing on them identifies your property, a plain key on a plain ring dropped in a park across town, the risk is low. Some people reasonably decide not to change the lock in that situation, though many still choose to for peace of mind, as the Guardian’s guidance on lost keys notes. 1
Be honest with yourself about the identifying details. A distinctive keyring, a fob with a car dealership’s name, or a key lost in your own street all shift the balance towards changing the lock.
Change the whole lock, or just part of it?
Often only the working part needs changing. On a uPVC or composite door, a locksmith can usually replace just the lock cylinder, the part the key enters, leaving the handles and mechanism in place. That renders the old key useless and is quicker and cheaper than replacing the whole lock. The same approach works for lost window and garage door keys. 2 On a wooden door with a mortice lock, the lock case may need replacing, but this is still a routine job.
A lock change is also a natural moment to consider upgrades, and it is worth asking about two things. Insurance: many home policies expect final exit doors to have locks meeting British Standard BS3621, so if your current lock does not comply, a like-for-like replacement keeps a weakness your insurer may care about. 2 And security: on uPVC and composite doors, a cylinder meeting the TS007 three-star or Sold Secure SS312 Diamond standard protects against lock snapping, a common forced-entry method. Our guides to anti-snap lock ratings and changing locks when you move house cover both in more detail.
If several doors need work, ask about having locks keyed alike, so one key opens them all.
What does a locksmith actually do?
If it is your car keys that are missing, that is a job for an auto locksmith rather than a house locksmith. If you are locked out of the house, a locksmith will normally get you in without damaging the door, then replace the cylinder or lock so the missing key no longer works, with brand-new keys supplied for the new cylinder. 2
Agree the price before work begins. There is no governing body setting locksmith prices in the UK, so charges vary with the lock type, the time of day and your area, and it is worth phoning more than one firm for a quote. 12 Our guide to what a locksmith quote should include explains what to ask.
How do I stop it happening again?
Once the immediate problem is sorted, a few cheap habits remove most of the risk. Have a spare key made and leave it with someone you trust nearby, never under a doormat or flowerpot. If you still have one working key, we can get copies of keys made for you. A small key safe fitted outside is a sensible alternative if there is no one nearby. A Bluetooth tracker on the keyring makes a misplaced set findable in minutes. And if losing keys is a recurring theme in your household, a key-operated lock is not your only option: a smart lock opened by code, card or phone, or another keyless entry system, removes the physical key entirely, though they bring their own considerations. 1
Frequently asked questions
Should I change my locks if I lose my house keys?
If the keys were stolen, could be linked to your address, or were lost near your home, yes, change them promptly. If they were lost far from home with nothing identifying on them, the risk is much lower and some people choose not to; most locksmiths will still recommend changing the lock as a precaution, because you cannot know who found them.
Can a locksmith make a new key without the original?
Usually you will not need one. When keys are lost for good, the practical answer is to replace the cylinder or the lock, and the new part comes with its own brand-new keys, so the original is never needed. If you still have one working key and simply want spares, we can get copies of keys made for you.
Is it cheaper to change the cylinder rather than the whole lock?
Yes, in most cases. On uPVC and composite doors the cylinder is usually the only part that needs replacing to make the old key useless, which is a quicker and cheaper job than replacing the complete lock or mechanism. Your locksmith can confirm what your particular door needs.
Do I need to tell my home insurance company if I lose my keys?
If the keys were stolen, or lost with anything identifying your address, tell your insurer; some policies require it, and theft may be covered. It is also the moment to check your locks meet your policy’s requirements, such as BS3621 on final exit doors, because a claim can be affected if they do not.
What should I do if I have lost my only set of keys?
You will need a locksmith to get you back in; emergency locksmiths work around the clock. Phone two or three for quotes, agree the price before work starts, and have the lock changed at the same visit so the lost key no longer works. Then have spare keys made (we can get copies for you) and leave one with someone you trust.
Sources and checks
- The Guardian, “What to do if your house keys are lost, and when you get new ones” (9 July 2025). Practical steps: retracing, spare keys, police reports, the change-versus-leave decision, renting, quotes and prevention.
- Master Locksmiths Association, “Lost House Keys: What To Do” (locksmiths.co.uk, undated, checked 19 October 2026). Trade-body guidance: changing locks as a security precaution, cylinder replacement on uPVC and composite doors, BS3621 insurance compliance, anti-snap upgrades, keyed-alike locks, and why prices vary.
Sources checked 19 October 2026. This is general guidance, not a security assessment of your home; a locksmith can advise on your particular doors and locks.