Nokia BH-900 Headphones User Manual

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Check that the headset is within 10 meters (30 feet) of your phone
and that there are no obstructions between the headset and the
phone, such as walls or other electronic devices.
To reset the headset if it stops functioning, although it is charged,
plug the headset into a charger, and briefly press the power key and
the middle of the volume key at the same time. This reset does not
clear your settings (for example, pairing settings).