Immobiliser key!??? Or is it?

[Jackson74]

I have this what looks like a microchip covered with protective plastic on my car-keyring. It looks like a plastic bullet! The key to start my car will only work with this thing attached my keychain or near to the dashboard, which makes me think its some sort of immobiliser key. Car will not work without it. A lot of my mechanically minded mates are quite intrigued by it but have never seen one before, but car is approx.15 years old. Anyone seen these before and anyone got any or let me know where I can get info on this thing, in case I lose it? Thanks in advance!

[BillyBB]

The enclosed bullet is the ID transponder that is often referred to as an immobiliser. In USA often termed VATS for Vehicle Anti Theft Sytem
They have been used in Europe by more and more manufacturers since the early nineties. There are many different types.
A good independent Auto Locksmith or the car dealer can produce a key with the chip built in. Sounds like your key is a duplicate, maybe they changed the mechanical lock but could not reprogram the ECU.