Sounds to me like the switch in the driver side lock is starting to go. If it happens again before you get it fixed, twist the key to the lock position with the driver side door open (it won't lock with the door open). That should disable the alarm... until you lock the door again.
FWIW, I can only set and disable my alarm from the driver side door, and I can only disable the alarm by unlocking the door, opening the door, and twisting the key to the lock position. It took some getting used to, but we're good friends now