Santacary HCHO Index Monitor, Formaldehyde (Oxymethylene) Temperature and Humidity Air Quality Pocket Indicator [FH20] Accurate AQI Datalogger Indoor DetectorTwo-year Warranty

I read a lot of reviews before choosing this handheld, and decided to go for it and return it if it didn't work. It is easy to use and the battery lasts a long time (multiple days). So does it work? Yes, but the readings seem to be higher than your actual formaldehyde levels. I sort of freaked out at the first readings -- like .7 or .9 ppms until I got accustomed to it. It works by diffusion and is very (cross) sensitive to alcohols (cooking chicken with white wine, spraying lysol in a room, or a closed cabinet with makeup and hair products) which it does explain in the instruction booklet. Does it sense formaldehyde? I had the opportunity to hold it side-by-side a "real" commercial grade sniffer and mine measured consistently .6 - .8 ppms higher than that one, so I think mine is just picking up more cross-contamination. Once you know that, I think it is reliable to show you your levels in one location relative to another -- and you can also see how levels increase with increasing temperature and humidity. I did get it to register close to 0 ppm outside on a very cool breezy (~62 degree) morning.

Very useful for the price.

The number goes up and down erratically in the same place. Looks cheaply made from China. The led lights are not in the correct place.

Works well and very compact.

worked fine for a week or so, then would not charge.