My 2000 Sable security system is going off at random times, on the average about once every couple of days. It can occur anywhere, anytime. It can occur whether the car is left locked or not. The dealer has had it 3 times and has had no success correcting the problem. (They replaced the hood switch, although I told them I didn't understand how that would cause the fault to occur even when the car was unlocked, and now they've disabled the hood switch. They say that's the only fault they're getting from the system diagnosis.) I would be happy just to have the darned system disabled, although repairing it would be even better. I've taken to pulling the horn fuse when I really don't want it to go off, but that's a pain to get to.
Another symptom is that a total of 4 or 5 times (i.e. rarely), the keys do not work to start the car, i.e. the behavior is as if you don't have the special key with the chip in it. After a few minutes (the system apparently resets) the keys work.
If anyone can provide advice, please do!