Review on Extech CO240 Portable Carbon Dioxide Quality Analyzer by Viswanath Lopez

Terrible, overpriced, unreliable, unstable and inaccurate meter. Would give a zero or negative* rating if I could. DO NOT BUY THIS EXTECH CO2 Meter. I bought three different CO2 monitors. An in house power supply from Gain Express, a battery from NewishTool and then Extech because it was a well known brand and more portable. Unfortunately, the $300 Extech was unstable from the start and needed constant recalibration. Much worse than $120-140 units. Then last week it started showing 6000ppm (outdoors!) after being calibrated just a few days earlier. And this week it started throwing error codes. And reading 136ppm 5 minutes after external calibration to 400ppm. The other two inexpensive devices, on the other hand, are solid, stable and perform well. Extech should be ashamed of selling crap like this. I would return it if it is not past the return date. I stuck with it. Definitely don't buy Extech. This isn't the first Extech device I've had issues with. We have similar VOC and HCHO testers that have also had problems. I bought again on a call and I was clearly wrong. Finally learned to avoid Extech.