How Many Spare Keys Should You Have for Your Home?
Most households should hold one key per adult occupant, one spare kept securely off-site with someone trusted, and no more. That is typically three to four keys for a family home. Every additional key beyond genuine need increases the chance of one being lost or copied without your knowledge. Keys should never be hidden outside the property, and any key you cannot currently account for is a reason to rekey.

Key management is one of those household questions nobody makes an active decision about. Keys accumulate. A set is cut when a child gets old enough to come home alone, another when a relative stays for a fortnight, another for the neighbour who fed the cat two summers ago. Nobody tracks them, and at some point the honest answer to how many working keys exist for your front door becomes I am not certain. That uncertainty is the actual security problem, more than any lock specification.
Working Out the Right Number
One key per adult occupant.
Everyone who needs independent access should have their own key. Sharing a single key between two working adults produces exactly the coordination problems that lead to keys being hidden outside or left with neighbours.
One secure off-site spare.
A spare held by a trusted person who does not live at the property is the single most useful key you can have. It resolves lockouts without a call-out, and it survives events that affect the property itself. A parent, adult child, or long-standing friend a short drive away is ideal.
Children old enough for independent access.
A key for a child who regularly comes home alone is a genuine need. A key for a younger child who is always accompanied is an extra key in circulation without a purpose.
That is usually it.
Three to four keys covers most family homes. Every key beyond that should have a reason you can state.
Where Spare Keys Should Not Live
Anywhere outside the property.
Under a mat, in a plant pot, on a ledge above the door, inside a fake rock, under the third step. Every location that feels clever is a location that is searched routinely by anyone who tries doors for a living. This is not a theoretical risk. It is one of the most common ways homes are entered without any force at all.
In an unsecured key safe.
A wall-mounted key box is only as good as its build quality and how it is fixed. Cheap key boxes can be levered off a wall or forced open with basic tools in under a minute. If a key box is genuinely needed, it should be a quality unit rated for the purpose and fixed into masonry.
In the car.
A house key in a vehicle parked at the property, particularly with any documentation showing the address, connects the two directly. Vehicle break-ins are common and the key is a bonus to whoever finds it.
Labelled with the address.
A key with an address tag turns a lost key into a targeted opportunity. Keys should carry no information that identifies the property.
Auditing What You Actually Have
Work through it honestly. List every key you know exists and who has it. Include keys held by adult children who have moved out, former housemates, tradespeople given access during works, cleaners, and anyone who has looked after the property while you were away.
Two questions matter. Can you account for every key on the list, and is there anyone on the list who no longer needs access. If the answer to the first is no, or the answer to the second is yes, rekeying is the appropriate response.
Rekeying changes the internal configuration of the cylinder so all existing keys stop working, and new keys are issued to exactly the people who should have them.
The Case for Restricted Keys
For households where key control matters more than usual — a property that has had extensive works, a home with high-value contents, a rental you own — a
restricted key profile removes the copying problem entirely. Keys on a restricted profile cannot be cut at a hardware store or kiosk because the blanks are not available. Copies come only from your
locksmith, only for people you have authorised, and every cut is recorded.
Frequently Asked Questions
Is it worth having a key hidden outside for emergencies?
No. The security cost far outweighs the convenience. A spare held off-site with someone trusted solves the same problem without leaving a working key on the property for anyone to find.
How many keys does a locksmith cut with a new lock?
Standard practice is two or three keys per cylinder. Additional keys can be cut at the time of installation, which is usually cheaper than having them cut later.
Should all the doors in a house use the same key?
Keying alike, where one key opens every external door, is a substantial convenience improvement and costs little or nothing extra when specified at installation. The trade-off is that losing one key affects every door. For most households the convenience wins.
What should I do if I lose a key?
If the key is identifiable to your address, or was lost somewhere near the property, rekey promptly. If it was lost far from home with nothing identifying it, the risk is low but you should still update your key count and consider whether you now have too few working keys.
Do I need to rekey after buying a house?
Yes. You have no way of knowing how many keys the previous owners issued over their period of ownership, or to whom. Rekeying on taking possession is standard practice and inexpensive relative to the certainty it provides.
Contact Malvern Lock Service on 0477-615-507 for key cutting, rekeying, and restricted key systems across Melbourne's inner south-east. Neale cuts keys to manufacturer code on calibrated equipment and can set up a restricted profile so no copy of your key can ever be cut without your authorisation. Over 35 years of experience. MLAA member and VIC Police registered. Serving Malvern, Malvern East, Armadale, Toorak, Prahran, South Yarra, Glen Iris, Camberwell, Glen Huntly, Hawthorn, Kooyong, St Kilda, St Kilda East, and Surrey Hills.