Product review (3 stars): Costs more to run due to the short battery life and expensive button battery.
It is not a bad unit, but you will need a lot of batteries.  I bought two different new Digital Thermometers at the same time.  The one which used the AAA battery is still running on the original battery while I've gone through several of the 'button' batteries on this thermometer.  Otherwise the unit performs OK.  I compared 4 thermometers at one time (two new, two older) all in the same location, all read a bit different for both temperatures and humidity, sometimes seemingly wildly different, but as a %difference probably ok.  The button batteries are not inexpensive either so this unit is not being used currently.