Product review (1 stars): Works well. Takes CR2032 battery. -- Update -- can't read display
Seems to work fine, but I haven't tried the salt in a bag test to see how accurate the hygrometer is. It's nice and compact, but I'm not a fan of the small CR2032 lithium battery it uses. I'd prefer if the unit were bigger and could use AAA or AA batteries which are less expensive. I'm pleased with this though.

***UPDATE*** - Reduced to 1 star... Display seems to have failed. Only part of the numbers are legible. If I apply a small amount of pressure to the display I can read it. I have other hygrometers that have worked for nearly 10 years. This one doesn't last.