The "Automatic Personal Signaling Reflector" works continuously and automatically 24-7, day and night. You can work on your shelter, gather food/water or rest if injured. Rescuers will not walk by you if you're asleep or if you are unable to respond. The highly reflective silver-coated plastic works with Sunligh, Search Lights and Flashlights. It's always working for you. No batteries to rundown.