PETZL NAO Rechargeable Headlamp with Self Adjusting Reactive Lighting Technology, Grey/Black, 187gm Headlamp with REACTIVE LIGHTING technology has a sensor to detect ambient lighting Customized lighting with OS by Petzl software allows the user to: regulate light intensity and lighting time and distance based on the activity etc. Li-Ion rechargeable battery performs well at low temperatures and easily rechargeable with the integrated USB connection Multifunction on/off switch can be locked to avoid accidentally turning it on when stored/transported Optional belt kit for NAO (E36R10) allows the rechargeable battery to be moved to the belt to reduce the weight worn on the head, or to keep it warm in winter