Great idea, but if it doesn't work...Bought one - worked out of the box - only had one false alarm - didn't have a range problem. But it stopped working one day - blinks red and green. Got a new battery, never got it to work again. So, I bought another one. This one has never worked. It was blinking red and green out of the box. Have tried different batteries, read and re-read the instructions (pushed the reset button). My guess - the transmitters fail. Now I have two units - neither works. If anyone wants, I'll sell them to you, at a great price - two for the price of one.