FM Radio headset with built in antenna to prevent snagging on equipment. 3.5 mm listen only stereo input (limited to 82 dB) for connection to external devices (e.g. mobile phone, radio, two-way radio and iPod). Auto power off turns headset off after 4 hours of non-use, to save energy and a low-battery warning informs you when to change batteries. To reduce the corrosion caused by sweat the electronics are located in the outer part of the cup. Battery life: 40 hours.