Mopeka Pro Check Universal Bundle - 2 Pro Universal Sensors and 2 Tank Halos - Wireless Propane Tank Gauge Sensor - BBQ and RV Must Have Accessories Monitors Outside Propane Tank Levels in your Camper

Why it's worth it

Two ultrasonic sensors stick magnetically to the bottom of your tanks and report the liquid level to a free app, with alarms you set yourself. It's the most trustworthy reading you'll get short of hauling the cylinder onto a bathroom scale.

Ultrasonic sensing is the only approach here that warns you before the tank is nearly empty. The sensor times the echo of a sound wave sent up through the tank bottom and works out how deep the liquid is. Mopeka puts the accuracy at about ±10%, roughly twice as good as the analog pressure dials that miss by 20% or worse. And because it reads liquid rather than vapor pressure, a cold morning doesn't wreck the number.

Setup takes a couple of minutes per tank. The sensor snaps onto the steel bottom with magnets strong enough to stay put on washboard roads, and the included Tank Halo ring keeps the full weight of the tank off the sensor body — skip that ring and you'll be re-centering the thing after every refill. The same sensors cover standard BBQ cylinders, RV tanks, patio heaters and custom LPG tanks up to 250 gallons.

From our review of 5 smart propane tank level monitors

What we like

• +Ultrasonic sensing is the only approach here that warns you before the tank is nearly empty
• +Setup takes a couple of minutes per tank
• +The free Tank Check app is the part owners keep coming back to
• +You won't be swapping batteries every season

What to know

• –It's Bluetooth on its own
• –There's some fussiness