When mounting Contact Sensors for the Boundary system on aluminium doors or windows, there is a little bit more to consider.
Sometimes aluminium can affect the range that these sensors can effectively operate from the central hub. This is because the radio signal can be reduced significantly. But the Boundary system has been designed to be compliant with British and European standards so the gap between the sensor contacts should be no more than 25mm or 1 inch. Any further apart and the sensor may not function as intended or easily create a false alarm. It is possible to mount the two parts on different shapes of frames, windows, and doors because the magnet can be mounted at an angle.
So we suggest where possible that you mount the magnet (the smaller part) on an aluminium door or window and the sensor on a wall. See the below image as an example.