BigDrops BigDrops Fuel Oil Sensor: The Oil Sensor screws into an existing bung on an oil tank and you're done. Wirelessly transmits data to your back office software every hour. It also has a 10 year battery life. Your total cost is only a few cents per day. BigDrops Propane Sensor: The Propane sensor is placed (with the magnetic mounts) onto the propane tank, plug it into a remote ready gauge and you are done. It wirelessly transmits data to your back office software every hour. It also include a 10 year battery life. Your total cost is only a few cents per day.