Instruct: Classify the given Amazon review into positive or negative sentiment.
Query: O2 Oxygen Bar

This unit is loud. I'm surprized no one mentions it. The noise is comparable to a portable 12v tire inflator. Is there any other oxygen generation that does not use a noisy compresser. How could you possible relax with a tire inflator two feet away from your head. When the unit turns off I cant begin to descibe the ADDITIONAL noise it makes and unless you get up to turn off the primary power switch (yes there are two power switches) you have to deal with ultrabright blinking blue led light. Restfull oxygen therapy twenty minutes before bed......yeah right.....you might as well be on a subway in the Bronx. Does it delivery 40% oxygen...probably....but after your session youll need 30 to 60 minutes to calm down befor you can sleep.