Used Car Keys Check: How Many Keys and Fobs Should You Get?

Imagine this: you’ve just bought a three-year-old hatchback. It’s great. Then you drop the only key down a drain. The dealer quotes you £280 for a new one, plus £90 to program it, and you have to get the car recovered to them. That’s a bad day. It’s also entirely avoidable with a proper used car keys check before you buy.

Why the keys matter more than you think

Modern car keys are not just bits of metal. They contain transponder chips, remote radios, and sometimes motion sensors. A replacement involves cutting a blade, buying a fob, and programming it to the car’s immobiliser. That’s why a missing key can be a £300 problem. And if the car has keyless entry, a lost fob is a security risk — anyone who finds it can drive away.

How many keys should you get?

The two-key rule

Never buy a used car with just one key unless you’ve factored in the cost of a spare. Two working keys is the standard. One key means you’re one mistake away from a hefty bill. Also check that both keys are full-function keys, not a valet key that only opens the doors.

What counts as a ‘working’ key?

A working key locks and unlocks the car, starts the engine, and operates the boot. Test both keys separately. If it’s a flip key, check the blade springs out and locks securely. If it has a remote, press every button. Don’t just assume — try them.

Testing every remote, fob and keyless entry/start

Physical buttons and flip keys

Press lock, unlock, boot, and panic (if fitted). Check the range — walk 10 metres away and try. A weak fob battery is easy to fix, but a failing fob isn’t.

Keyless entry and push-button start

Stand a few metres away and approach the car. Does it unlock automatically? Try all doors, not just the driver’s. Get in, press the start button with the fob in your pocket. Then try the emergency start method: hold the fob against the start button and press. This is what you’d need if the fob battery dies. Check the manual for the exact spot.

Hidden key slots and emergency start

Many keyless cars have a hidden physical keyhole under a plastic cover on the door handle. Find it. Make sure the key blade fits and turns. If the car has a keyless start, there’s usually a backup slot or sensor.

Checking for aftermarket alarms and immobilisers

Why aftermarket systems can be a red flag

A factory alarm is fine. An aftermarket one might have been fitted after a theft attempt, or by an owner who didn’t trust the original. They can cause battery drain, random immobiliser faults, and electrical gremlins. They can also void your warranty if not fitted properly.

How to spot them

Look for extra fobs on the keyring, an LED light on the dashboard, a toggle switch under the dash, or non-standard wiring. Check under the bonnet for a siren or extra horns. Ask the seller directly: ‘Has it got an aftermarket alarm or immobiliser?’ If they don’t know, that’s a warning sign.

Replacement and reprogramming costs: what you could be facing

Standard remote key replacement

A basic remote key from an independent auto locksmith costs around £150 to £250. A main dealer might charge £200 to £300. That includes the key, cutting, and programming.

Keyless fobs and smart keys

These are pricier. Expect £200 to £400 for a smart key, plus programming. Some premium models can be £500 or more. If the car has keyless entry and start, you really don’t want to lose a fob.

Programming and coding

If you supply your own key, programming is typically £50 to £100 at an independent. Dealers often charge more, and some cars require dealer-only coding. Always ask if the car can be programmed by a third party.

Aftermarket vs dealer

Independent auto locksmiths are usually cheaper and can come to you. But for some newer cars, only the dealer can program a new key. Do your homework before you buy.

A pre-purchase checklist you can use on the test drive

• Ask for two keys. If there’s only one, negotiate.
• Test every button on every fob.
• Test keyless entry from a distance and try all doors.
• Try the emergency start method with the fob.
• Check for aftermarket alarms, immobilisers, or extra fobs.
• Look for warning lights, odd wiring, or a hidden kill switch.
• Ask for the key code or security tag — it makes replacement easier.
• Get any key-related promises in writing before you pay.

The trade-offs: older cars vs modern keyless

Older cars with simple keys are cheap to replace but easier to steal. Modern keyless cars are more secure but replacement costs are high. Keyless cars are also vulnerable to relay theft, where thieves boost the signal from your fob inside the house. A Faraday pouch costs £10 to £20 and blocks the signal. If you buy a keyless car, budget for one.

What to do if the car only has one key

Use it as a bargaining chip. A replacement key costs £150 to £400, so ask for that amount off the price, or ask the seller to supply a second key before you buy. If they refuse, walk away or factor in the cost.

The takeaway

A used car keys check takes ten minutes and can save you hundreds. Confirm two working keys, test every fob and keyless function, look for aftermarket security systems, and know what replacements cost. Don’t let a missing key be the thing that ruins your new car honeymoon.

When you’re ready to make that change, have a look at UpCars.uk — every car there is checked over properly before it’s listed, so you can start your own key check from a solid starting point.