Product review (5 stars): USE NEW BATTERIES.
USE NEW BATTERIES.  I had nothing but trouble with this.  I had transferred the batteries out of the old thermometer receiver I was replacing.  Using old batteries in the receiver makes it look like the sensor is not working.  When I put in new batteries, it worked perfectly.

Also, and this is important, if you live where it gets down to 0F, put lithium batteries in the sensor.  Alkalines will freeze up at about 0F.