Mini Digital Thermometer 2-Pack Hygrometer Indoor Humidity Monitor Temperature Humidity Gauge Meter with Fahrenheit (℉) for Humidors, Greenhouse, Garden, Cellar, Closet Etc by DWEPTU

Double-Check Thermostat Accuracy
I live in a very warm climate and I don’t have central air conditioning, just window units, and I was concerned they might be running unnecessarily. I love these little guys- they fit just about anywhere (I stuck one on top of my thermostat) and the sticky pads work great. They confirm that my AC is working properly and when winter comes, I’ll be able to save on my gas bill for the heater. They are very accurate and I trust what they are telling me. I’d like to have one in every room and at this price, I can do that and I definitely recommend them.

GOOD LITTLE THERMOMETERS, I USE TO MONITOR HVAC OUTLET TEMPS
Handy little stick-on thermometers with humidity also. I bought these to stick to corners of our HVAC outlets in our desert home to monitor multiple central A/C outlet air temps especially when outside air temps reach 110-115 degrees. Having these stuck to the corners of the air outlets makes it much easier to check outlet air temps versus walking around using my infrared temperature gun to point at outlets from time to time or guessing if the central AC units are putting out cold enough air just by feel. These are not real big so are a little difficult to read in dim light, but they are fine for what I need them for. I checked them against a few other indoor thermometers and they appear to be pretty accurate. HVAC techs should provide these to homeowners with central air so they can accurately assess how well their HVAC units are working on an ongoing basis as far as providing cool enough air. Everything I read says shoot for outlet air temp in the range of15-20 degrees below ambient room air temp. When I was using my infrared gun last year I saw one of our rooftop HVAC units (which does half our house) was putting out “cold” air that was only 8-10 degrees below room temps, so I had the HVAC people over. They cleaned the coils and condensers on our rooftop HVAC units and added a little refrigerant and that fixed the problem 100% and the outlet air for that HVAC unit then came out 17-22 degrees (slightly different from outlet to outlet) lower than room temp air.  

Needs Study (on humidity display)
The units seem good. May not be all matching values due to tolerance, but there is something I just started noticing as I’m getting deeper into using them, that worries me.I noticed when reducing humidity, that the unit jumps from 25% to 16% directly. At the crossing, I saw the display jumping back and forth between 25% and 16% until it stabilized on 16% as the humidity gets drawn out of my system (with desiccant bags). This observation gave me confidence in thinking that the unit is not capable of showing intermediate values, hence, this was the resolution it could provide (at those humidity levels). So how many steps does the humidity display has between 1% and 99%? just 8 steps? 5 steps? what values are they?This makes me concerned that at low humidity ranges, the resolution of this device may not be good enough for some applications. It makes me happy when I think that the unit may be potentially using a calibrated lookup table to report fairly accurate humidity values, but the lack of resolution (going from 16% to 25% with nothing in between) makes me worry about this resolution issue maybe getting even worse at lower humidity (does it have one more value (say 6%) and that’s it? or is it going to stop at 16%? Time may tell for me, if my desiccant bags are able to further reduce humidity, but how to tell?)I believe these type of units (there seems to be many versions of this device, perhaps all with the same sensor/electronics guts inside) are in need of some analysis study that would let us, end users, know what to expect. I do not have the equipment to do such, and hope someone with interest would share a basic study, or maybe a link if it has been already done. I know that we get what we pay for, I just would like to improve a bit on the question: what did we paid for?Bottom line: How much money (and time) will we end up spending, to determine if we can rely on these units? I already know they don’t quite work the way we ‘assume’ they will work (there is no claim on displayed resolution, reading step size, etc. so it’s like a “what you see is what you get” kind of deal…)==============================6-Month Update:After about 6 months of use, I confirm the humidity reading at the low ranges is not more than a coarse circumstantial number, not to be taken literally.I confirmed this with other devices I bought that are more expensive, with BLE wireless connectivity, etc. Maybe these little low cost devices are more reliable for higher humidity values, but for low ranges, it can measure over 15% discrepancy (if it was an offset I could work with them, but the readings seem to be erratic around the actual humidity level). Depending on your use case, this could be OK, for example you just need to know if it is going over 30% and that’s it. In that’s the case this device may the job.For me, this is the end of the road with these little devices. I will keep on having them on my home AC vents, until the batteries die, but since my use case is low humidity for 3D printer filament, they do not help me much for my time invested in keeping the filaments dry. I am turning to 2x to 4x more expensive devices now. To keep my review true to my experience and in an effort to be as transparent as possible I now reluctantly reduced my rating from 4 to 3 stars (because at first I was happy with them), to reflect this 6-month experience.There is nothing wrong with them considering they sell as low as 99-cents each in large quantities. I believe it is impressive that people could buy such technology including housing, sensors, processor, LCD, and even batteries for the money. Incredible! I thought I could use them, and it turned out I can not. My sealing system deteriorates with time and need re-dehydration, and these particular low cost sensors will not let me determine when I need to re-dehydrate.(I aimed too low, and had to rethink my strategy).Hope this helps,