We always recommend buying a balloon inflator that has a pressure gauge included. It displays how much helium remains in the tank. The pressure gauge will only provide a reading if the tank is open. Some pressure gauges display when the tank is empty, with lines or markings that will read full or empty based on the pressure in the tank. However, even when the gauge reads empty, the tank can still be used for as long as balloons continue to inflate. If a helium inflator or tank does not have a pressure gauge, you can tell that your tank is nearly empty when balloons inflate much slower.