The Key You Never Tested: What a Dead Spare Fob Really Costs
Photo: Geographer , CC BY-SA 2.0, via Wikimedia Commons
There is a drawer in most UK homes that contains a spare car key, a dead AA battery, a takeaway menu and a screwdriver that does not fit anything. The spare key is the thing we trust without testing. It came with the car, so it must work. Then the main fob gets dropped in a puddle, the battery dies at a retail park, or the keyless system decides it cannot see the fob, and the spare gets pressed into service for the first time in four years. That is when you find out it was never really a spare at all.
A key is not just a piece of metal with a button on it. It is part of the immobiliser system. The blade turns the lock, but the transponder or keyless receiver has to be recognised by the car before the engine will start. If the spare has been sitting in a drawer while its battery quietly drained, or if it was never programmed properly in the first place, it will not help you when you need it most.
The ten-minute spare-key test
Do this at home, not on a forecourt with the engine running and a queue behind you. Start with the main key and the spare. Check the physical blade opens the driver's door and, if the car has one, the ignition. Then test the remote buttons: lock, unlock, boot release if fitted. Stand a few metres away and see how the fob responds. A remote that only works when you are right next to the car is often a sign of a failing battery or a weakening receiver.
Next, put the key in the car and start it. For a keyless car, bring the fob inside, press the brake and the start button as normal. Then switch off, lock the car, unlock it with the spare, and start it again. Do the same with the main key. You are not just checking the battery; you are checking that the car still recognises both keys. If one starts the car and the other only unlocks the door, you have a programming or transponder issue, not just a flat cell.
Finally, check the spare's battery. Many fobs use a CR2032 or similar coin cell, and they are cheap and easy to change. Look in the handbook for the correct type and the battery change procedure. Some fobs need to be opened carefully with a plastic trim tool, and some keyless fobs have a hidden physical key inside. If you are not confident, ask a garage to change it while the car is in for a service. It takes minutes and avoids cracked casings.
Early warning signs worth listening to
A fob rarely fails without giving you a hint. The first sign is usually range: you have to stand closer to the car, or press the button two or three times. The second is inconsistency: it works in the morning but not after the car has been parked in the cold. The third is the dashboard message. 'Key not detected' or 'smart key not found' is the car telling you the receiver is struggling to hear the fob.
Cold weather makes weak batteries weaker, which is why so many key problems show up in November and December. Water damage is another common cause. A fob that has been through the washing machine may work for a while and then corrode inside. Buttons that feel mushy or need a hard press are also a warning. If the spare has been stored with the buttons pressed against something in a drawer, the battery may have been draining for months.
Emergency starts and the handbook trick
If the fob battery is flat but the car recognises the key, many keyless cars have an emergency start method. Usually you hold the fob against the start button or a marked area on the steering column while pressing the button. Some cars have a hidden key slot or a receiver pad in the centre console. The exact procedure varies, so read the handbook before you need it. Do not rely on a YouTube video for a different model and hope for the best.
If the remote is dead but the blade works, you can usually unlock the door manually and start the car with the key in the ignition, provided the transponder is still recognised. If the car is keyless-only and the fob is not detected, the emergency start method is your best bet. If neither works, you are into recovery or locksmith territory. That is why the ten-minute test matters: it moves the discovery from a rainy car park to your driveway.
What a replacement really involves
A replacement key is not just a blank blade. It has to be cut to the car's lock and programmed to the immobiliser. Some cars need a diagnostic session and a security code; some need all keys present; some can be done by a mobile auto-locksmith. Dealers can usually supply and programme a key, but they are often the most expensive route. Independent garages with the right diagnostic equipment may be cheaper, and a reputable auto-locksmith can often cut and programme on your driveway.
Costs vary widely by make and model. A simple remote key for an older car might be a modest spend, while a smart key for a newer car can run into hundreds of pounds, especially if you have lost all keys and the car needs to be recovered. The questions to ask are straightforward: Is the price for supply, cutting and programming? Does it include VAT? Will the new key work with the existing immobiliser? What happens if the programming fails? Do you need the car present, and do you need all existing keys? Get the quote in writing before anyone starts.
Also ask about proof of ownership. A legitimate locksmith or dealer should want to see the V5C and your ID. That is not an inconvenience; it is the thing that stops someone else ordering a key for your car. If a deal sounds too cheap and nobody asks for paperwork, walk away.
Make the spare a real spare
Test both keys at every service, or at least once a year. Change the fob battery before it becomes a problem, not after. Keep the spare at home rather than in the car, where it can be found or affected by heat and cold. If you have a keyless car, consider a signal-blocking pouch for storage at home, but do not let that replace basic key security. And if the spare has never been used, use it for a week. A key that never turns is a key that never gets tested.
The cheapest key is the one you already own and know works. The most expensive one is the one you had to have cut, programmed and delivered by a recovery truck on a dark November evening. Ten minutes in the driveway is a much better deal.
