It’s Saturday morning. Your car’s on the drive, but the only key you own has gone missing. A few years ago, that meant a trip to the hardware shop to get a new one cut. Today, it usually means a transponder chip, a remote key fob and a car that refuses to start for anything it doesn’t recognise.
An auto locksmith can identify your exact key type, cut a new blade to match your car’s locks, then plug specialist equipment into your car’s diagnostic port to program the new key’s chip and remote into the immobiliser. Any lost keys can be wiped from the car’s memory at the same time, so they won’t start it if someone finds them.
Here’s how that works in practice, step by step, and what you can do to make the job quicker and cheaper.
Why modern car keys can’t just be copied
Older car keys were simple metal blades. When cut to the right shape, the car would start.
That changed when immobilisers became compulsory on all new vehicles sold in England and Wales in October 1998. Since then, almost every car key has carried a tiny electronic chip called a transponder. When you turn the key or press the start button, that chip sends a code to the car’s engine control unit. No recognised code, no start, even if the blade is perfect.
So, replacing a modern key is two jobs, the physical part that opens the doors and the electronic part the car has to accept. If you’d like a plain-English guide to the terms locksmiths use, our auto locksmith glossary covers them.
The four types of car keys we see most
Knowing which key you have will tell you roughly how involved the replacement will be:
Transponder keys
A metal blade with a chip hidden in the plastic head. There are no buttons. You lock the doors by hand. These are the most straightforward modern keys to replace.
Remote keys and flip keys
A transponder key with a built-in remote for central locking. On many cars, the chip that starts the engine and the remote that locks the doors are two separate systems, and each must be programmed.
Remote fobs with a hidden emergency blade
Common on newer cars. The fob does the work, but there’s usually a small metal blade tucked inside for the door if the battery dies.
Smart or proximity keys
Keyless entry and push-button start. The key stays in your pocket, and the car detects it nearby. These need the most specialist equipment, and the replacement fob usually costs more.
How an auto locksmith replaces your key, step by step
Every car is a little different, but a professional replacement follows the same basic pattern:
1. Identifying your car and key
First, we confirm your car’s make, model, year and registration, and check which key type and chip your car uses. Getting this right matters. A key that looks identical can carry the wrong chip or transmit on the wrong frequency, and it won’t talk to your car.
2. Checking you own the vehicle
A reputable auto locksmith will always ask for your V5C logbook and photo ID before making a key. It protects you. A locksmith who’ll happily make a key for anyone is a locksmith who could make one for a thief, too.
3. Cutting the blade
If you still have a working key, the blade can be copied from it. If every key is lost, the locksmith can work out the cut from a key code or by decoding the car’s locks, then cut it on a computerised machine. Many modern cars use high-security, laser-cut blades rather than the old, notched style, so the right machine makes all the difference.
4. Programming the chip and remote
The locksmith connects programming equipment to your car’s diagnostic (OBD) port, usually under the dashboard. That gives secure access to the immobiliser, so the new key’s chip can be added to the list of keys the car will accept. The remote locking buttons are then paired, which, on some cars, is a separate step.
Reprogramming a car key typically takes between 30 minutes to an hour, depending on the make and model. Cars where every key has been lost can take longer, because there’s no working key to start from.
5. Removing lost keys and testing
If your old key is lost or stolen, it can usually be deleted from the car’s memory during programming. After that, it won’t start the engine even if someone finds it. Finally, everything gets tested, including starting, locking, unlocking, the boot and the remote’s range.
You can read more about what’s possible in our guide, ‘Can you reprogram a car key that’s already been programmed? ’.
Get a spare car key before you need one
Most of the stressful car key calls we get could have been avoided with a spare car key.
When you still have one working key, adding a second is the easier, cheaper version of the job. Wait until that last key is gone, and you’re paying for an ‘all keys lost’ replacement, often while you can’t use your car at all.
So, if you bought a used car that came with one key, or you’ve been getting by on a single fob for years, sort a spare now. Our guide ‘Do you have a spare car key?’ explains why it’s worth doing.
We’d also add one thing most guides skip. The equipment used to program keys is powerful. The Metropolitan Police estimates that electronic devices are used in around 60% of vehicle thefts in London, and the Crime and Policing Act 2026 now makes possessing or supplying a device for vehicle theft an offence carrying up to five years in prison. That’s a good reason to use a vetted, accountable locksmith who checks who owns the vehicle. Our guide to common locksmith scams shows what to watch for.
Replace, repair or reprogram?
Not every faulty key needs replacing. Before you pay for a new one, it’s worth checking what’s actually wrong:
- The remote has stopped, but the car still starts: often a flat battery or a worn button. See ‘What to do if your remote car key stops working’.
- The case is cracked, or the blade is loose: the electronics can often be moved into a new shell. Read ‘Can you repair car key fobs?’.
- The car won’t recognise the key at all: the chip may need reprogramming, or the key may be faulty. Our guide to what causes a car key to malfunction goes through the usual culprits.
Auto locksmith or main dealer?
Many drivers assume only the dealer can supply a key for a modern car. For most makes, that isn’t the case. An auto locksmith can cut and program keys for a wide range of vehicles, and a mobile locksmith comes to you, so there’s no need to arrange recovery to a dealership when your only key has gone. For a side-by-side look, see our replacement car keys: garages page.
There are some newer or premium models where a dealer is the better route. If that applies to your car, we’ll tell you straight away rather than take on a job we can’t finish.
Quick questions
What should I have ready?
Your V5C logbook, photo ID, and any working key you still have. The registration number helps us confirm the right key before we arrive.
Can a used fob from another car be programmed to mine?
Sometimes, but not always. Many fobs can be programmed only once, so a second-hand fob can be a false economy. Check with us before you buy one.
Will my old key still work after I get a new one?
A key you still have can stay programmed. A lost or stolen key can usually be removed from the car’s memory so it no longer starts the engine.
Need a replacement car key in Nottingham?
Our MLA-certified locksmiths cut and program replacement car keys and fobs for most makes and models. Give us a call on 0115 942 2315 or visit our auto locksmith services page to find out more.