Be very aware, at the time of my purchase seller did not inform of how the detectors were powered. As it turns out you have to options; #1 Hard wire from your alarm, since this sensors are normally for the perimeter you will need to run tremendous amounts of wire( and double that since they are two units!). #2 Buy two separate power sources. So the item, for me, has no use. Seller did not offer any alternative solution
Looking bigger than expected. Have not tested them yet.