Abstract: A warning device configured for removable mounting in combination with a high pressure gas cylinder and a regulator used to regulate the high pressure gas supplied by the cylinder. The device compression mounts between the regulator and tank outlet on conventional portable oxygen and gas supply systems using a specially configured manifold. The device features one or a combination of alarms, from a group including audio, visual, electronic, and remotely transmitted alarms. These alarms are activated by a pressure switch monitoring the remaining supply in the gas cylinder through a conduit the manifold. The alarm signal from the device alerts the user, or a third party monitoring the user, of current tank pressure or will sound an alarm when remaining high pressure gas inside the gas cylinder drops below a predetermined level.