Product review (5 stars): Ignore those negative ratings...they just didn't read the product details.
I'd give 5 stars twice to make up for those other two stupid negative reviews.  Every one of the complaints listed on their reviews are spelled out in the product details.  Although they say they do not come with batteries, the two I received had batteries.  I felt kind of silly trying to remove the plastic cover that I thought was the fake numbers like they do on clocks when I realized, nope...the numbers changed in front of me.  :0)

I tied the two sensors together and they were very close in their readings, well within the stated parameters.  Oh, and the instructions the guy complained were not included - the number with the "C" next to it is the degrees in Celsius, and the number with the "%" next to it is the percentage of humidity.  Oh, and if the LED dies, it's time to replace the batteries.

I have a bearded dragon and use these to monitor the insect breeding bins to make sure the temp and humidity are in the right ranges to keep them nice and healthy.  Works perfectly for my needs.