The ET120 is it the perfect choice for HVAC professionals. It is an easy-to-use tester that provides audible and visual alarms in the presence of methane, propane and other combustible gases at concentrations as low as 50 ppm. It features two levels of sensitivity depending on users needs. High (approximately 50 to 1000 ppm) and Low (approximately 1000 to 10000 ppm).