The Inogen One G5 portable oxygen concentrator is remarkably quiet, with a noise level of up to 38 decibels, or the equivalent of a quiet library. It has up to six levels of oxygen flow settings and is ideal for those who need more than level five settings. The Inogen One G5 Pulse Portable Oxygen Concentrator is a better alternative to oxygen tanks and gives you better capability to do more things and be more independent. Use the double battery (separate purchase) to give it up to an incredible 13 hours of operation. The Inogen One G5 has six flow settings and is an FDA-approved portable oxygen concentrator device that is helpful for individuals suffering from chronic obstructive pulmonary disease or those suffering from low blood oxygen levels.