JS-7910 is a lens for Jablotron's JA and JS PIR detectors. The lens is for people with pets, so the PIR detector is not disturbed by the pet's movements on the floor. If you install it at a height of 2.5 meters, there will be a free area 7 cm above floor level 7 meters outside.
Please note that the lens is not compatible with Jablotron's JA-111P xx and JA-151P xx series.