The Mopeka TankCheck is a magnetic sensor that mounts to the bottom of the LP tank to indicate the level of propane left in the tank. The sensor works via Bluetooth to send readings to the TankCheck app on your smartphone or device. The app can support multiple tank monitors at once. The level is updated every 5 seconds when your device is within 150' of the sensor.• Magnetic sensors mount to the bottom of the LP tank• Updates every 5 seconds• Use with 20, 30, and 40-lb. propane tanks• Sensor communicates via Bluetooth to a smartphone or tablet• Free TankCheck app can monitor up to 15 different tanks• Shows tank level using percentages• Sensor uses a #CR2032 button battery• Kit comes with 2 magnetic sensors and 6 propane tank feet Communicates via Bluetooth to your smartphone or tablet Sends updated readings every 5 seconds Includes 2 magnetic sensors & 6 propane tank feet | AP Products Mopeka TankCheck LPG Dual Sensor Kit in Blue