This CO alarm is very nice to look at. Everything you need to know about the feature is clearly displayed on the 3-inch round screen. A large and brightly lit display shows you the amount of carbon monoxide present, as well as the temperature and humidity in the environment. Very handy if you are a herpetologist or need to keep your tarantula in optimal conditions. But is what is shown correct? The humidity shown matched exactly the amount shown on my smart thermostat. According to the thermometer I trusted, the temperature was a little off. I was looking for a method to calibrate, but unfortunately this device does not support this function. Exact temperature accuracy doesn't matter much - detecting carbon monoxide is what really counts. My unit reads ZERO ppm carbon monoxide - that's reassuring. Since this unit is so portable and can be charged with a standard 5V USB phone charger, I will take it with us on our small RV trips. The RV has a propane heater, stove and refrigerator, so an O2 monitor is a must. What I like about this CEKKIENA carbon monoxide alarm: - The look and feel - The portability and ease of use. - The display can be switched to "always on" or "off after ten minutes". - Color coded light indicating different levels of CO detected. (Green = OK, Yellow = 100-200ppm, Red + Siren Alert = over 200ppm) - Celsius or Fahrenheit display - 90 hours of use on one charge. Cons: Not really negative, but this unit cannot be wall mounted as the USB port is on the back of the unit. There is a fold-out stand on the back of the unit so it can be placed on a shelf, countertop or mantel. When traveling with the mobile home, it should be in a drawer. I'm really glad I have this...a little bit more security for my family - and I look forward to using it in the RV.