To work properly the Jawbone's sensor must be in constant contact with your cheek. That requires a really good fit. The sensor must also, obviously, be sensitive. Unfortunately, of half a dozen headsets I've used, the Jawbone is the hardest to get even a poor fit--its usual mode is falling out. And, the sensor wore out of a few months of knocking around in pockets, meaning that even if I used one hand to press the headset into (through) my face, it eventually wouldn't even then work--ruining what I first thought was finally, finally, the end of my search for a passable headset.