AP Products AP Products 024-1000 Tank Check LP With Monitor Kit

Sensor magnetically mounts to bottom of tank
Tank level is updated every 5 seconds via Sonar/Ultrasound Technology
Sensor communicates to Bluetooth enabled mobile device, tablet or monitor in coach
Free downloadable app can read up to 15 sensors; YOU can download the app on IOS or Android phone to monitor the tanks.

Receive alerts live on your phone - when your tanks are low.
Standard Sensor: 20, 30 and 40 DOT cylinders and horizontal RV tanks
3 year warranty

Comes with 2 sensors and 1 monitor as shown.  
What people are saying about these sensors: "No more guessing at tank levels! Are these sensors strictly necessary? No, of course not! There are other, cheaper, and free ways to check your tank level. You can just pick up the tank and see how heavy it is. You can pour a cup of warm water down the side of the tank and see a line where the liquid level is. You can buy a gauge that attaches to the valve at the top (don't do this, they are very inaccurate). I have even pointed an infrared thermometer at the tank - the area of the tanks with liquid will always be a different temperature than where the tank is empty.  That said, my wife has this weird anxiety about running out of propane. Our trailer has two 30lb bottles and an auto switching regulator. We also have a pretty small travel trailer. Even during the winter when we are running the furnace, I could probably go 45 days on the two tanks. Every evening before bed, and several times after I was long asleep, she would have a panic attack and make me go outside and pour a glass of warm water on the tank to verify that that furnace just turned off because the thermostat told it to, and not because we ran out of propane and we are about to freeze to death. Enter these tank sensors. Each is roughly the size and thickness of half a deck of playing cards. On one side there is a small rubber pad, about the size of a dime, and two strong magnets. to use them you simply lay your tank on its side for a moment, clean off any accumulated gunk off of the bottom, and stick it on with the magnets so that the rubber pad is as close to the center as you can get it. Each sensor has a green button on it. The first time you use them, you have to press the button 5 or 6 times in a row, very quickly, to take it out of shipping/battery saver mode. You only have to do that one time. When you download the accompanying app from the iOS App Store, or the Google Play store, the app will 'see' the sensors and give you a chance to configure and name them.In our case, I connected them one at a time so that I knew which tank was which. The app defaults to 20lb tanks, so I had to change it to match my 30lb ones, and I named the tanks "Driver Side" and "Passenger Side". Now, when my wife is worried about propane, she can just pick up her phone and see the exact levels.Note that the sensors are very picky about placement and about the tanks themselves being level. Before our most recent trip I had the truck and trailer parked out in front of the house, at the curb. With the passenger side tires in the gutter, the trailer was tilting very slightly to the passenger side. Parked like this, one of the tanks showed 6%, even though I had just had it filled. Once we were at the campsite and level, it correctly showed 100%.The sensors seem to work using something very much like sonar. By attaching to the bottom of the tank, they can emit a "ping" up through the liquid propane, which is reflected back by the surface of the liquid. The less liquid you have, the lower the surface is, the faster the ping makes it back to the sensor. it's actually super simple and has the potential to be very precise.Caveats:* These guys communicate via Bluetooth. So you need to be within Bluetooth range to get a reading.* Because the tanks are steel, they tend to kill the range, so the sensors come with a set of aluminum clips that you attach to the base ring on the tanks. They act as "feet" to raise the tank by 1/4 inch to improve reception. These things are incredibly flimsy. My kit came 8 of them for two tanks, and 3 broke while I was installing them. They do sell plastic rings that attach to the bottom of the tank which are supposed to be more durable, but they are $14 each and I can't bring myself to do that yet.* The sensors are only held on by magnets. If you regularly remove the tanks to take them to be refilled, you either need to handle them very carefully and not bang them around (and potentially lose a sensor), or remove the sensors and reinstall when you put the tank back on.* If you use those "tank exchange" services at the 7-11, you have to remember to grab your sensor and move it to the new tank.One of my sensors was defective out of the box. It read between 3% and 6% regardless of propane level, how level the trailer was, or if it was even attached to a tank. I did quite a bit of troubleshooting and testing before I contacted the manufacturer, just in case I was doing something wrong. I filled out the support form on their website and they responded via email within a couple of days. They asked for my mailing address, and sent me a new sensor, along with a prepaid shipping label to return the bad one. They also said that they would replace the aluminum spacers, but they didn't - so I am a little annoyed about that.All in all, would I buy them again? Yes, absolutely. They are easy to use once they are set up, they give my wife peace of mind, and if I'm honest, it makes me feel a little better too - being able to see that I have 37% remaining, as compared to lifting the tank up and thinking "That's still about half full...."
These things are really slick!
Reviewed on July 15, 2020