Portable Oxygen Concentrator Broken?

Hello everyone. I apologize in advance as I'm no expert on these things. I just picked up an Airsep Lifestle Portable oxygen concentrator for someone other than myself. When I turn it on it produces air just fine. After about 2 minutes the alarm goes off (a red light starts blinking and beeping.) I don't have any tubes to test it with. Could it be because the unit isn't detecting a pulse? Thanks for the help!