What is an immobiliser and why won't a spare key start the car?

By Michalis Manoli, Manolis M. Key Services, Aglantzia · 1 November 2026

If you have ever had a spare car key cut at an ordinary key-cutting shop and found that it turns in the ignition but the car will not start, the reason is almost always the immobiliser. Below we explain in plain terms how it works and what it takes to get a key that works properly. For all our car services, see the page Car keys and immobilisers.

How does an immobiliser work?

In the head of the key there is a tiny chip, the transponder. When you put the key in the ignition or press the start button, an antenna around the ignition “reads” the chip. The car's ECU checks whether the code is one of those it has stored. If it is, it allows the engine to start; if not, it cuts the ignition or the fuel supply, and usually a key or padlock warning light flashes on the dashboard.

Since when have cars had immobilisers?

In the European Union, immobilisers became compulsory on all new cars from 1998. So almost every car on Cyprus's roads today has an immobiliser, including many used imports from Japan or the United Kingdom.

Chip, remote or smart key: what is the difference?

• Chip (transponder): allows the engine to start. It does not need a battery.
• Remote: the buttons that unlock and lock the doors. It needs a battery and its own programming.
• Smart key (keyless): the car unlocks and starts at the press of a button, as long as the key is nearby. It combines the chip and the remote in one.

A key may have a remote that works and a chip that is not programmed, or the other way round. That is why we always check both.

Why won't my spare key start the car?

1. The chip has not been programmed to the car.
2. The wrong type of chip was fitted for that particular model.
3. The chip has been damaged by a fall, water or damp.
4. With a smart key, the battery is low and the car does not “see” the key.

How is a new immobiliser key made?

1. Cutting: we cut the metal blade of the key on a machine, so that it fits the locks and the ignition.
2. Programming: using diagnostic equipment connected to the car, we “teach” the new chip to the ECU.
3. Remote: we programme the buttons for unlocking and locking.
4. Testing: we check the ignition, the doors and the boot.

If all the keys have been lost, we make a new key from scratch, without a sample. We can also erase the lost keys from the car's memory, so that nobody else can use them.

Dealer or locksmith?

There is no need to go to the dealer or wait for a key from abroad. A locksmith who specialises in immobilisers and has the right equipment does the same job, often on the same day. One of our customers wrote on Google that he dropped by the shop for a second car key and was done in 15 minutes.

Tips for immobiliser keys

• Always have a second key. It is much simpler to copy a key that works than to make a new one when they are all lost.
• Avoid drops and water; the chip and the remote's circuit board are delicate.
• Replace the remote's battery as soon as you notice it getting weak.
• If you lose a key, ask for it to be erased from the car's memory.