'Return the unit the value is expressed in.'

@property
def unit_of_measurement(self):

    if (('current_sleep' in self._sensor) or ('last_sleep' in self._sensor)):
        return 'Score'
    elif ('bed_temp' in self._sensor):
        if (self._units == 'si'):
            return '\xc2\xb0C'
        return '\xc2\xb0F'
    return None
