Immobilizer (car security) warning light: what it means.
A small key or car-with-padlock light. Flashing slowly when the car is parked is normal: it means the anti-theft system is on. If it stays on or flashes fast and the car won’t start, the car isn’t recognizing the key.
Can I keep driving?
If it is flashing slowly while parked, that’s normal. If the car won’t start, don’t force it: the anti-theft system is stopping the engine.
What to do
Try the spare key. If that works, the first key’s chip or battery is the problem.
Take any other keys or fobs off the key ring, as they can interfere with the signal.
Replace the battery in a key fob if it’s a remote-type key.
Wait a minute or two, turn the key to on (not start) and try again.
If it still won’t start, a dealer or locksmith can re-program the key.
General guidance, not a diagnosis. Warning lights vary between cars, so check your owner's manual too. If you're ever unsure or the car feels wrong, stop and call for help.