code: public function setAway($away_mode, $serial_number = NULL, $eco_when_away = TRUE) {
          $serial_number = $this->getDefaultSerial($serial_number);
          $data = json_encode(array('away' => $away_mode, 'away_timestamp' => time(), 'away_setter' => 0));
          $structure_id = $this->getDeviceInfo($serial_number)->location;
          if ($away_mode == AWAY_MODE_ON && $eco_when_away) {
              $this->setEcoMode(ECO_MODE_MANUAL, $serial_number);
          } else {
              $this->setEcoMode(ECO_MODE_SCHEDULE, $serial_number);
          }
          return $this->doPOST("/v2/put/structure." . $structure_id, $data);
      }
docs: Change the location (structure) to away or present. Can also set the specified thermostat to use ECO temperatures, when enabling Away mode.
  
  @param string $away_mode     AWAY_MODE_ON or AWAY_MODE_OFF
  @param string $serial_number The thermostat serial number. Defaults to the first device of the account.
  @param bool   $eco_when_away Specify if you want to use Eco temperatures or not, when using AWAY_MODE_ON. Default to TRUE.
  
  @return stdClass|bool The object returned by the API call, or FALSE on error.