Review on GrillPro 00030 Magnetic Gas Level Indicator: Effortlessly Monitor Your Propane Tank Levels by Ronald Reese

Works as advertised. I bought 4 of these at this price to fit a 100lb tank (stacked on top of each other as they are only 4 inches tall). The magnet only measures the temperature of the surface below and is therefore only as accurate as the temperature difference across the surface of the tank. In order to show the actual temperature difference in the liquid/gas line, the tank needs to work for a while. As a result, the liquid cools down through evaporation (basic thermodynamics). the liquid gets cold enough the tank next to the liquid gets colder than the tank next to the air above the liquid level magnets simply measure the temperature of the tank, do not directly measure the actual liquid level If you run the tank long enough you can see condensation (water) outside or even frost (when it gets really cold and the room is not too warm) where the liquid level is. This works great, but you need to know the actual measurements for it to "work". If the entire magnet is above the liquid or air portion (the line is above or below the magnet) it will read a constant temperature and you will think it is "not working". Or if the liquid hasn't had time to evaporate to give a significant temperature difference, you won't see anything on the magnet either - but that's not the sensor's fault.