My 57 Captiva has developed an intermittent problem with the alarm. 30 seconds or so after locking the car with the keyfob, the alarm goes off. After unlocking and re-locking a few more times, it will finally keep quiet. I'm sure it's done this with both sets of keys so I don't think it's a keyfob issue. The car doesn't get used very much and I'm wondering if there's a failing battery in the alarm unit. Anyone got any ideas?