i have just brought a used mazda mx5 and the immobilser is like a small round disc its not attached to a key or a card, its like a small round battery, i'm afraid i might lose it, should it be attached to a key or a card? tia
Yes it should be, normally a small plastic thing like a small tennis bat! There is a chip inside this button and if you aint got a spare you could be locked out.
I had one of these and lost it for a week, and my spare key wouldn't work without it. Nightmare!! I eventually found it otherwise I was stuck. I sellotaped it hidden inside the car afterwards, luckily my car was that rubbish no-one would have stolen it!