PH-100AHC Active Noise Reduction (ANR) Headset is designed for Helicopter pilots who take flying seriously. Using the newest sound technology,Active noticeably reduces cockpit noise up to 52db. So you can fly longer, more comfortably, in a quieter environment. Battery Box With S/M Switch.The headset will shut-off automatically when the headset is unplugged from the battery box or is manually turned off using the toggle switch on the battery box. The headset will also automatically turn off when the radio or avionics master switch is turned off.