rear view mirror has fallen off

somebody been fixing their lipstick?

You will need to remove the old mirror pad 1st, then clean both the areas of contact with surgical spirits etc to get rid of any dirt/gease. One both surfaces are spotless, use a new mirror pad pressing it back on firmly but dont go mad or you could possibly crack the windscreen.

I had the same thing happen a couple of years ago. I had to have a new screen and a few days later, in the middle of the night, I was woken by my alarm going off with the car in the garage. I went down stairs and unlocked and opened the door between the house and the garage and used my remote to stop the alarm. I opened the car and everything seem to be OK. Must have been a false alarm I thought. It was only the next day when I backed the car out of the garage I realised there was no rear-view mirror. It was laying on the floor in the passenger foot-well. The interior movement sensors had detected the downward movement of the mirror and set off the alarm!