Invisible Bluetooth Earbud , BTERIF&reg; Ultra Small Bluetooth 4.0 Earbud compact Headset with microphone Earphones Support Hands-free Calling For two Smartphones Simultaneously The Newest bluetooth headset with lightweight and compact portable design.Simple and Stylish. Built in HD and Sensitivity microphone. Idea for in car calling or working use. Perfect for Stealth Listening or watching at work. The size of this bluetooth Headset is derived from the test date of our engineers which it will be suitable with most persons' ears. Built-in 50mAh polymer battery. Up to 4 hours of continuous talk time, 3.5 hours of music time Can connected with two smartphone at the same time, the wireless range up to 10 meters