A kegerator is a draft beer system housed inside a refrigerator. The main parts of a kegerator include the refrigerator, beer keg, CO2 tank, regulator, shank, draft faucet, beer line and air hoses. The CO2 tank is a crucial piece of kegerator equipment, responsible for keeping beer fresh and carbonated for four to six months. Without it, your beer would only last A day or two and you'd need a hand pump to drain it from the keg. Your regulator gauge will warn you when your CO2 tank is empty. Several other signs may accompany the gauge reading.

Read the regulator gauge on your CO2 tank. Some regulators have two gauges -- one that shows the air pressure and one that shows how much air is left in the tank. Some regulators have only an air pressure gauge. All gauges will read zero when your CO2 tank is empty.

Look to see how fast your beer is flowing out of the draft faucet when you pour it. The beer will flow out of the faucet in an unusually slow manner when your CO2 tank is empty because the CO2 is responsible for pushing the beer out of the keg and into the faucet.

Drink the beer that comes out of your kegerator faucet. It will taste flat, lacking the usual fresh brewery flavor, when your CO2 tank is empty. CO2 maintains the carbonation of kegerator beer.

Check the head (foam) on the beer that you pour from your kegerator. A head with large, soapy-looking bubbles or foam that disappears quickly are signs of an empty CO2 tank.

Keep track of how many kegs of beer you use after you refill your CO2 tank. A five-pound tank of CO2 lasts for five to seven half kegs of beer. If you come close to this estimate and your kegerator is showing other signs mentioned above, your CO2 tank is empty or close to it.