Now that the summer weather has arrived, I like leaving the patio doors open, but I also want to work on the computer upstairs. What I'm looking for is an alarm of some kind that would sound if an intruder crossed the threshold into the house. It would probably have an infrared beam or possibly be ultrasonic. It would need to be portable, e.g. attachment via sucker or clamp, so that it could be removed easily.
Anything like this in the sheds?
MM