Walker’s Razor Slim. SAC is a special electronic circuitry that will compress gun shots and other loud noises down to a safe level, without completely shutting the noise off. This allows you to hear range commands or communicate with your hunting partners, even when shots are being fired around you. Includes 2 AAA batteries. Ultra low profile ear cups. Full dynamic range HD speakers for clear balanced sound. Low noise/ frequency tuned for natural sound clarity. Single knob volume control. Sound activated compression circuit (SAC). 0.02 second response time.