I found that in the place where this was to be fitted by the inside doorway, it was in too bright an area.
I belive that this item works on detecting a diffrence in light being reflected back into the reciever.
What I did was to fit it into a box 50mm deep, 100mm high with open bottom and access hole on one side to be able to operate the on - off switch.
This cured the problem and it now works in very bright sunlight. The range is as stated at a touch over three metres.
for the price good value. All i need to monitor is battery life but this will obviously depend on usage.
Very good value.