I absolutely love my Quantum, it's knocked everything out of my front pocket, but I do have a strong concern. The head is really easy to twist. A few weeks ago, I took my light -- with recently charged battery, barely used -- out of my pocket, and it barely emitted any light. Put the battery on the voltmeter, sure enough, it was low. I'd imagined the light was getting warm in my pocket a few times, obviously it had turned itself on a few times. Okay, duly noted, I started turning the light off with a full half twist off... But 2 weeks later, same thing, pull out light, battery is low. Once may be an accident, but twice, considering this is an unprotected battery, puts me in the "permanently shelve" category for this light. I'm giving it one more try, and turning it off with an even longer twist, will see what happens