My 1986 190E 2.3-16 has developed an alarm problem. About a week ago it started chirping the horn - one very short chirp - when I armed the system by locking the door with the key. This would occur at either door or the trunk, so it wasn't the actuator in the lock. Now the gremlin has grown - any time I lock the car with the key, the alarm will sound.

I currently have the battery disconnected in the hope that the system will reset itself, but I'm not holding my breath.

Any help?