AlexofAz wrote a review of Mammut S-Lite Headlamp on July 13, 2014
Familiarity: I've used it several times
It uses only one AA battery, hangs around your neck like a puka shell necklace, and is always ready when it gets dark. One battery means one back up battery instead of 4 plus 4 backups. It doesn't require any tools to change the battery, but it's not water proof or even resistant as the trade off. That said, it's always around my neck when I hit the trail.