If you've ever been quoted different prices for key replacement on different vehicles, or wondered why your car needs a locksmith with special equipment while your parents' old Fiesta doesn't — it all comes down to the key type. Here's what's actually going on.
The Basic Cut Key (Pre-1995)
Before the mid-1990s, car keys were simple: a shaped metal blade, no electronics. The lock mechanism recognises the blade shape and either turns or doesn't. A locksmith can cut a replacement using a blank and a profile — no programming needed. These are cheap and quick to sort, but also easy for thieves to copy.
The Transponder Key (1995–present)
In the mid-1990s, insurers pushed manufacturers to adopt immobilisers after car theft peaked. The solution was the transponder key: a conventional metal blade with a microchip embedded in the plastic head.
Here's how it works: a ring aerial around the ignition barrel continuously broadcasts a low-power radio signal. When the key enters, this energises the microchip via induction (no battery needed in the key — the aerial powers it). The chip broadcasts back a unique code, the immobiliser ECU checks it, and if it matches a registered code, the fuel system is enabled.
A key cut perfectly to fit the ignition but with no chip — or with an unprogrammed chip — will turn, but the engine won't start. Both cutting and programming are required.
The Remote Key Fob (2000s onwards)
A remote key fob is essentially a transponder key with an integrated remote control for the central locking. It has its own battery (usually a CR2032 coin cell) to power the remote transmitter. The transponder chip itself still works via induction from the ignition ring.
Replacement involves cutting the blade, programming the chip to the immobiliser, and separately coding the remote to the car's body control module. If the battery dies, the remote stops working but the key still starts the car.
The Smart Key / Proximity Key (2010s onwards)
Smart keys (also called proximity keys, keyless entry keys, or intelligent keys depending on the manufacturer) work differently. Instead of being inserted into the ignition, they stay in your pocket. The vehicle constantly broadcasts a short-range signal and detects the key's presence. When you touch the door handle, it unlocks. When you press the start button, it starts.
The encryption is more sophisticated than a standard transponder key, and the two-way communication uses rolling codes (the code changes after every use) rather than a fixed code. Replacing a smart key requires deeper ECU access and more sophisticated diagnostic equipment, which is why it costs more.
Quick Reference
| Feature | Transponder | Smart Key |
|---|---|---|
| Physical blade required | ✓ Yes | ✓ Hidden blade |
| Key inserted to start | ✓ Yes | ✗ Stays in pocket |
| Chip battery needed | ✗ No (passive) | ✓ Yes |
| Programming required | ✓ Yes | ✓ Yes (more complex) |
| Replacement cost | Lower | Higher |
| Vulnerable to relay attacks | Less so | Yes — use signal blocker |
What This Means for Replacement
When you call an auto locksmith about a replacement key, telling them your vehicle's make, model, and year is the quickest way to get an accurate quote — because that determines the key type. If you're curious which type you have, look at your existing key: if it has buttons and a thick plastic head, it's a remote fob or smart key. If it has no buttons and a thin plastic head, it's a basic transponder key.
For our full transponder key programming service and car key programming in Ashton-in-Makerfield, or for a cost comparison by key type, see our 2026 car key replacement cost guide.