I have an after market immobiliser on my disco but only one fob.

Are replacements general purpose or (as I suspect) specific to the manufacturer? I have the original invoice and have contacted the original installer but no response (to be fair it was installed a while back).

I'd rather not replace the whole thing just to get a second fob, but the immobiliser can only be disabled with the fob, so if I break/lose the one I have I'm fooked

In the case of worst case... anyone recommend an good installer in the NE Hants area?