FWIW: I tried a digital thermometer/hygrometer unit designed for a terrarium and discovered the hard way that the hygrometer didn't work if the humidity was below 40% OR the temperature was above 95. To be fair, it did say so in the fine print on the instruction sheet, but that was a little late to help since I bought it off ebay.
Yes digital hygrometers may not be reliable.
I am using one from Wmart, but also double checking with old fashioned analog mechanical hygrometer, you can get a combo therm and hygro in wmart too.
They are not always calibrated right, but mine works fine showing increase or decrease of humidity confirming digital one reading.