Have a 2002 Sonata, Sometimes the car locks the door by itself. Once when the keys were in the ignition! My guess was it had something to do with the car battery getting weak. I put a new battery in and the problem stopped. But just the other day it did it when I unlocked the car using the remote key (but I never opened the door) Has anyone else had this happen? is it a Hyundai thing?

 

Yes, the car will re-lock the doors if you unlock it with the remote but don't open a door with 30 seconds.