[r800v6]

This may be too late or no help at all but here goes-

If the remote stops working and you need to disengage the alarm/immobiliser Open the drivers door with the key the alarm will be triggered and the horn/siren will sound.
Wait until the horn/siren has sounded for 30 seconds, then start the car within 10 seconds of the alarm stopping sounding, the alarm will now be disconnected.
If you fail to turn on the ignition/start the engine on the first try within the first ten seconds you can try again as many as 7 times, after the seventh consecutive time the car can no longer be started as the alarm will be permanently on and will then require the use of the remote to deactivate.

This method will only work if the car has been unlocked with the key and no other sensors have been activated prior to this (obviously to ensure the person has the key and is not breaking in and activating the ignition by other means)

Hope this helps,
Paul.