Product review (5 stars): It works!
This works as advertised!  Add batteries, put a nail or hook somewhere, put the smaller sensor outside, or where you want to record the temperature, turn on the main unit, and it works.  I don't know the maximum distance between the sensor and read-out, but it works at 50 feet through the ceiling and two walls in my house.  The read-out unit can be wall-mounted or just placed on a flat surface.  Both of my units are inside (sensor in the attic which I want to monitor).  I don't know if the sensor will withstand months of exposure to bright sunlight, freezing, rain, etc.  I expect it will because it looks well made.  The read-out is about 5 inches high, with a simple screen, readable at a convenient distance.