The left button is to open the side tone function of the headset, that is, the environmental sound is transmitted to the headset through the microphone, and of course, your own voice will be transmitted, so that some important sound reminders are not so easy to miss, but it is still recommended that in the use of active or passive noise-cancelling headphones, it is best to make sure that you can receive reminders such as phone calls or ringtones. Make sure you are safe in the environment when using outdoors.
