Car unlocks on it's own?

[ryushe]

Hi there,

Just bought a very nice looking LHS with only 34k miles on it two days ago, but I've noticed a very disturbing problem. When I park and lock it, I can come back a few hours later and the driver front door will be unlocked! I am VERY sure I locked the car down.
This worries me, as it makes it hard to park when it's not in the garage, and even then I don't like it. Anyone have this happen as well?
I suspect it's an electrical issue, but for the life of me can't find an electrical wiring diagram or manual anywhere. If there's anyone out there that has one and is willing to share, please reply below

edit: I just did the status code check trick and got 12, 41 and 55.
The 12 and 55 don't concern me much, it's the 41 that might be an issue. I'm not a very technical person, so what exactly is meant by "Charging system excess or no field current"?

Thanks for your time folks.

[taillight]

Bad alternator. Have it checked.

[ryushe]

Would a bad alternator be a reason for the door to unlock by itself? Or would that be an unrelated problem to the code 41 I got?