Product review (1 stars): TRASH
I wish I listened to the bad reviews on this, because they are true.
I purchased these hoping it would be sufficient to keep track of things until I was able to purchase and set up a permanent solution for heat and humidity monitoring an emergency reptile rescue situation.
These have been in use for 3 weeks. One never reads above 77.7 degrees F for temperature despite many controlled tests.  Comparing the reads on these to instant reads on 2 different temp guns they are never correct, typically reading 5-9 degrees colder than the temp gun and my other digital thermometers, occasionally 4-7 degrees higher.  Would give 1 star but they have been accurate within 2-3% consistently with humidity which was the ONLY reason I chose these over ones that did not gauge humidity.

Update: Within a few days of the original review the humidity started to show huge variants. Tested against a trusted digital they were all off by 17-38%.

tl;dr Save your money, these are absolute garbage and not even worth something to use in a bind. The most useful part of this product will be the batteries salvaged from them.