The HDC 451 NoiseGard mobile set are open stereo headphones with active noise compensation for mobile applications. Powered by two AA batteries, these headphones reduce ambient noise by up to 10 decibels. This functionality protects hearing and reduces stress. The headphones terminate in a standard 0.125-inch miniplug for portable audio systems, plus a 0.25-inch adapter is provided for connecting to home stereo systems and a 2x-mono adapter for airline audio and some other devices.