The Razor Slim XTRM series features cooling headband a noise Rrduction rating (NRR) of 21 dB and utilized sound activated compression (SAC) of 0.02 seconds. 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.