The Mopeka Check Standard Sensor works on 20, 30, and 40 lb (5, 7.5, and 10 gal) DOT cylinders, and on horizontal RV tanks. Allows you to monitor the level of propane using the free Mopeka Check app on your smartphone or tablet. Or, propane level can also be monitored with the stand-alone Mopeka Check Double Monitor. Fuel level accuracy to within 1%. Adjustable low fuel level alert. Wireless connectivity with Blue Tooth 4.0 or better. Free App download to any smart device. App is able to monitor multiple Sensors at same time.