Alarm retrofit has gone horribly wrong..

[percodan]

06/2002 4.4i

I have successfully retrofitted navigation and Bluetooth, and both went smoothly. Since I park on the street and have had a window broken before, I thought an alarm would be a good addition (not standard for euro-spec). I used the official retrofit instructions and parts from ebay. Mirror with LED fitted, siren fitted, tilt sensor fitted, hood switch fitted, unfortunately connector for ultrasonic sensor is beyond reach from the hole in the roof, so I may need to drop the headliner - but the alarm should work without it. I have coded with P.A Soft BMW Scanner 1.4, and the LED on the mirror behaves correctly.

Problem is - the instant I unlock the car, the siren sounds. Siren goes 30 seconds on, 10 seconds off, for about 5 minutes. I can unplug the siren, and it keeps going. I can start the car and drive away, siren keeps going. I can re-arm the car and the siren keeps going. My best guess is that the siren is thinking it has been disconnected from the car the moment it is unlocked, but I can't figure out why it arms itself, but won't disarm.

My best googling suggested that the siren was faulty, so I replaced it with another one. Straight after installing I could arm and disarm without the siren going, however after being connected overnight and charging the internal battery, I had the same problem..

Someone please help - I'm at a loss!