Product review (4 stars): A low-cost, fairly-accurate humidity range monitor with alarm
This is a product that I've needed for some time. My only wish is that it had a louder alarm, though that would perhaps require a line-powered (rather than battery-powered) device.

The humidity measurements are surprising accurate for such a low-cost device. I've checked the unit repeatedly against an (>$100) HVAC-technician digital hygrometer that does the required wet-bulb dry-bulb dual sensing and computation. Apparently from the name of this product, it likewise does a dual measurement, though not to the accuracy of the high-end instrument.