Ahh, a new symptom for my poor car. Today apparently was the day when the keyless entry (Chapman aftermarket alarm) system decided it wasn't going to play nice with the power locks anymore.
Here's what I've done: Read all related archived entries on alt.autos.subaru that might be remotely (no pun intended) related. Played around with the remote and manually locking the driver's door with a key.
Findings: Found that the remote is still sending a lock/unlock signal to the door (I can hear it) The car can easily be locked/unlocked with the key. Unfortunately for me, I almost never use my keys on the door locks so if it can't be fixed cheaply/easily I will have to relearn a new habit.
**Preexisting conditions:** For many years now, the driver's side door lock inside switch cannot be manually locked or unlocked. I believe it broke once upon a time with some combination of me opening the door and either bumping the remote or I had my hand on the door lock. If I want to unlock the car doors when the car is running I must open the driver's door or pull on the handle just enough to get the doors to unlock.Also, the rubber-covered spring that tells the dome light to come on has been broken for probably as long as the driver's inside lock - my errant seatbelt got caught in the door and the plastic smashed enough that it worked poorly for some time and doesn't seem to work at all anymore (light does not come on when the driver's door is opened but does if any other door opens). It happened to seem more bent than usual today, but I don't think it's causing the problem.
Possible diagnosis: I have next to no electrical training besides some crappy physics classes I was forced to take years ago... nonetheless I don't think it's an electrical problem. I think the problem could relate to the driver's inside door lock but I don't understand why, after so many years that the problem should worsen.
Here's the weird thing. IIRC, the way I found out that there was a problem was that I used the remote to unlock/disarm today like I always do. I needed to put some items on the left rear seat, but that door's lock didn't unlock while the other 3 did. I unlocked it manually by reaching around inside. That was the last time that the remote unlocked/locked any doors. I don't know if it is significant in any way, but there it is.
Awaiting your sage advice, Rebecca