DYNAMIC BT Bluetooth headband ear muff hearing protection. Utilizes Bluetooth wireless technology to connect to Bluetooth enabled devices – most notably the users smart phone. Has a very good noise reduction rating of 24 SNR (CSA) and a very slim, lightweight design which allows for extended periods of use. The distance the muffs can be from your smart phone in order to work properly is approximately 10 meters. The DYNAMIC BT headphones have an integrated lithium ion battery that allows for up to 38 hours of use once fully charged. Allow 3-4 hours for the headphones to fully charge (comes with usb cable for charging). Another convenient feature is the ability to take phone calls while using the DYNAMIC BT headphones.