Top positive review
15 of 17 people found this helpful
on November 19, 2010
calibrates itself every 22 hours with a push of a button. alarm sounds at two different settings;low and high. monitor doesnt actually readout h2s levels, only alerts when it registers certain amounts. excellent monitor to use if you only need to know when h2s is present. not the monitor for you if you want to know an exact reading....such as 30ppm,37ppm,41pp, and so on......