'Return the device state attributes.'

@property
def device_state_attributes(self):

    data = {}
    if (self.signal is not None):
        data[ATTR_SIGNAL_STRENGTH] = self.signal
    if (self.time_in_state is not None):
        data[ATTR_TIME_IN_STATE] = self.time_in_state
    if (self.sensor is not None):
        data[ATTR_SENSOR_STRENGTH] = self.sensor
    if (self.access_token is not None):
        data[CONF_ACCESS_TOKEN] = self.access_token
    return data
