Why car locks to be divided into two locks
For safety, nothing more, because someone off the door may be very light, and then do not care, driving on the road is very dangerous, so the two door locks. Now a lot of cars are electric door.
I guess it is also estimated that the second level is used for insurance, or is a backup, a lock is not locked and the second level, so that the safety factor increased
The first level in fact play a similar role in the latch, you can make the door closed, rather than locked (open the door without the key), the second level is really locked door, open the door need key (or remote control)
