Our dads used the old lift-the-propane-tank-and-guess-how-much-left-method when it came time for cookouts. Surprisingly, it’s not a great method. You can take the guesswork out of cooking with propane with a Smart Gaswatch ($30). The tank sits on the scale, and you clip the display to the rim of the tank. Since there’s no actual connection to the tank, there’s no chance of leakage. An alarm also rings when you’re down to 20%, 15%, and 10%.