It's also easy to prevent any drain by unscrewing the tail cap just a bit (very little required). I'm not personally worried about the negligible parasitic drain but I do frequently back off the tail cap just to prevent unwanted activation of the light while in a backpack.
I have a BD Storm that has a lockout feature that requires you to hold a button for 6 seconds for lockout and another 6 seconds to undo lockout.
A fractional turn of the tail cap on the Zebralight is a much easier and I think a more elegant solution.
It is a beautiful light! It makes my other headlamps look clunky by comparison even though they are all nice headlamps :)