Review on Vaupan 4 Pack Mini Digital Thermometer Hygrometer - Indoor Temperature Humidity Monitor with LCD Display (Fahrenheit ℉) for Humidors, Greenhouse, Garden, Cellar, Guitar Case, Fridge - Black by Angie Wooten

This is the 3rd batch of sensors of this type and I have found that they are all of the same quality. You really shouldn't expect these to be lab-quality gauges, but they tend to operate with baseball field accuracy and more relative measurements. they all work fine. I think the idle ones just weren't making good contact with the battery and actually have an advantage - they tested a little higher (1.41V) than the working ones (1.35-1.36). Suffice it to say the meters have been running since they left China, so the 'new' batteries aren't the best. On the other hand my first set has been going for over a year now and is still running on the first batteries so I wouldn't look for a batch right away until I see some glitches. Apparently they work quite efficiently even at low voltage. The attached picture shows this set next to a random set I previously purchased. Depending on the use case, you can draw your own conclusions.