Charge before using! (The connecting process has been introduced in the manual with details, please read it before using the earphones)If no sound in one earphone, sync the earphones as described in the manual:1. Set up two earphones in the status of red and blue lights interval flashing both , and then click twice in one earphone. 2. If the light of one earphone turns dark, then the matching process is complete.3. Now searching earphones devices in the smart phone to complete the connection process.(The connecting process has been introduced in the guildance book with details, please read it before using the earphones)How to pair :1. long press left and right button together until two LED light flash red and blue alternataly.2. Double click either side button , wait one LED light flash red and blue alternately. 3. Search "TWS-i7" on bluetooth and pair it on your phone.IF you buy a pair,Please Note:1. For incoming call,only the master earbud has sound (This safety feature allows you to hear the traffic While driving)2. Keep away from wifi, route or other high frequency transmitting equipment to prevent interruption of signal receiving.