Why a red light continuously blinks, showing symbol of a lock even if I remove ignition key from the car and shutting down all the locks?

Security system error.If you newly replace any section that does do connect to car security system ,then you need to reprogram the security PC program .New key ,new switch,new PCM ,new door lock or new remote control must reprogram in order to car go out of the lock mode . For this matter you need to contact dealership or lock smites to reprogram the security system .

Ain’t theft that’s normal

Hi so this will be the service light ignore it at your peril. as the management system is telling you it needs to be looked at as servicing is what keeps the car in tune. so ignore it and after so many miles the system will shut down the engine so it will not go fast any longer. protecting itself and you the driver from a possible failure like a brake failure.

The battery in your key fob needs replacing

On my Fords, it indicates that the Theft Deterent System is active.

Try a different key or FOB.

which type of car

First guess, it shows you that the alarm system is working. Try reading you car manual, that will explain all of this to you.

It's the anti-theft system.