Door Ajar Chime
The "Door Ajar" chime is a feature available in Grand Theft Auto IV. The "Door Ajar" chime can be heard in some cars when the player leaves the vehicle with the door open. As it is very hard to hear, the best way to hear it is to go to a quiet area and to turn the volume up.
This is very realistic as most vehicles will not allow you to leave it open in real life as well.