PATS=Passive Anti Theft System.

It utilizes RFID (the same way contactless payment works)

There is a transponder within your key, that is paired with your car, the immobilizer is then disarmed.

It requires no power, that is for the remote C/L.

There will be an LED inside the car, this should extinguish when the ignition is switched on?

Do you not have a spare key you can try?

Martin