I have a X Reg Fiat Multipla, how to do you alarm your fiat multipla if the remote button on the key doesnt work any more.

you need to buy a new key and have it programed in,cheaper option,buy a second hand key and get it programed in to work the cent locking and alarm only,as the key can not be programed to start the car cos the chip do not match the ecu[cos it comes from a different car/ecu]in the latter case,you will need to carry both keys on one key ring.