Oxygen Concentrator
This is an electrically powered device that separates the oxygen out of the air, concentrates it, and stores it. This system has a number of advantages because it doesn't have to be refilled and it is not as costly as liquid oxygen.
Extra tubing permits the user to move around with minimal difficulty. Small, portable systems have been developed that afford even greater mobility.
You must have a cylinder of oxygen as a backup in the event of a power failure. You should advise your electric power company in order to get priority service when there is a power failure.