That's an excellent idea. Hearing accidentally-set-off car alarms has become so frequent that most of the people I know just ignore it, thus reducing its use as an anti-theft device.

Unfortunately, I doubt most thieves really want the car, anyway. More likely, they want the aftermarket radio, or the cash, purse or credit cards left laying visible.

So...leave most of the car alarm mechanism the same. The only difference would be putting the noisemaking part inside the cabin of the vehicle, and make it loud enough to hurt.

The only concern would be the risk of the thief filing a lawsuit against the owner for psychosematic hearing loss.

It could disable the car, lock the doors, and call the cops.

It's not a good idea to disable a driver after a car has been put in motion. Anyway, an external car alarm prevents much of the damage to the car.

I once saved my car from being stolen by putting a simple electric switch between the keyed ignition switch and the distributer. When I parked the car I pushed the switch to disable the system. The switch was disguised as a bolt head and placed in an inconvenient place beside the driver's seat. The thieves tried all sorts of tricks to start the car but did not discover the interrupted electric connection.They manually pushed the car some distance from my house but since they could not start it, finally left it there for me to find later. A clever thief could probably beat the simple system but probably most thieves would just choose another car to steal.

Good idea as long as the rightful owner can immediately disarm the alarm once the alarm becomes audible to him/her upon accidentally setting it off.

I was not talking about an alarm. I disabled the car from starting.

I was responding to the idea-originator, not your post. Sorry for any misunderstanding.