Hi. The button is a remote control which can be used for pause/play or pick up phone/put down phone.
Please note that this type of headphone is made for use with smartphones. The remote functions are what makes 4 poles on the 3.5mm jack plug necessary. If you use it with hifi sources, or any other source that uses a 3-pole output socket, the 4-pole plug on the headphone will give you trouble. This is because the extra pole will make a short with the ground connection in the source. There are converter cables on the market that can be used to change the 3-pole output to be come compatible with a 4-pole headphone. We do not carry those, but cable manufacturers make them. Also, some Nokia, Sony and other phones use a different sequence of poles in the socket, making it impossible to use JBL headphones. These telephones must be used with special headphones, specified by the telephone manufacturer. We hope this helps.
Date published: 2017-12-02