I have two alarms on mine, neither of which work satisfactorily. I have bought a new Scorpion alarm system which will replace both,but I'm not looking forward to removing the old systems. Tracing the wiring is hard with one system never mind two. From experience, a fair bit of space is needed as various bits of trim around the dash area need to come out. It helps if you have the installation guide for the system you are removing.... they can usually be found online. They are not particularly complex in operation. They usually inhibit the starter motor and/or fuel pump. Apart from that, it's things like operating central locking, flashing indicators and sensors on the bonnet oh! and sirens.