Sav-A-Ship is the model of a portable temporary life support generator. It could be carried by explorers or parties who would board starships who lacked life support or had gone off-line. One typical generator would have warning alarms for temperature, atmosphere and radiation.
Some models were unreliable, being prone to breakdown without warning. Harry Mudd carried one such generator when he boarded an alien derelict ship in the Harrapa system. (TOS video game: 25th Anniversary)