Product review (3 stars): I do not recommend this unit to anyone
I purchased this to get a reading from the inside of my safe without opening the door. I put the batteries in and set both the monitor and the outdoor gauge side by side.  the inside humidity read 43% and the outside read 42%. both components were sitting side by side in the same conditions.  the temp also was about 10 degrees off from one another. I do not recommend this unit to anyone
I did leave them side by side for 24 hours and still had different temps and humidity readings.  I ended up drilling holes in the casing of the outside probe and waited another 24 hours. magically they then read within 1 degree and 1 % humidity. as I am using this for a remote reading inside my safe and not outdoors, it ended up working well for me.