immobiliser is too effective! - nutty_nissan
Decided to use spare key on my GS300 since main key was somewhere upstairs in the house.

Went to unlock the car by placing key in lock and alarm goes off. Got inside and somehow the alarm eventually went off.

Found main key again, but car would not start. Thought battery was dead, so called breakdown people. They came, said it was an immobiliser issue since the red security light kept flashing, even after unlocking the car. The bloke said it would have to be towed back to Lexus on Monday morning.

Eventually, someone told me to try disconnecting the battery, then reconnecting, and turning the key to ignition position and leaving it there for at least 6 minutes. Then take out and retry starting the car. This procedure helps the key learn the car again, whatever that means.

Voila! It worked! Still don't know what the issue was with the spare key, but just shows you how immobilisers can be too effective if you don't know enough about the car.
immobiliser is too effective! - nutty_nissan
I would say at least 100 quid is how much Lexus would have charged me to do the 6 minute thing!