Product review (5 stars): These are perfect
These are perfect.  I especially like them in the cellar or lower-level bedroom, to help me determine how effective a dehumidifier is. For me, a room humidity of 40% seems to be fine, but I don't see any benefit in running the dehumidifier constantly, to get it down to 37%.  Yes -modern dehumidifiers have their own humidity level controls.  But when you push them to their limits, and especially if the coils begin to frost up, it it hard to get consistent results.  So these $10 (or less) digital meters on the other side of the room are an effective enhancement to the $200 appliance.