1998 Toyota Camry . Central locking issue
 

I have a problem with my central locking security system . I locked the door one day at the shopping center . Came back out about ten minutes later . Turned the key to unlock the door and it wouldn't . Tried again and again until the alarm came on . I can get into it now via a rear door that has had issues since I bought the car . This doesn't stop an ever present sound from the security system trying to lock me inside the car while I drive it though . Any ideas on how to fix and what to check first . My guess is it's the lock tumbler . But hoping not as deep as the locking solenoid