The Remote Sensor option allows you to locate the LBW-420 Ammonia Leak Detector panels outside the area to be monitored and the sensor from either panel to be remotely installed inside the area to be monitored. This gives you the safe advantage of remotely reviewing and acknowledging the Pre-Alarm and/or Alarm externally from the source of the alarms. The Remote Sensor can be installed a maximum of 500 feet away from either the LBW-420 Ammonia Leak Detector panels. The in-stock Remote Sensor comes standard with a NEMA 4X box, circuit board with sensor socket, and 50 feet of cable. Any additional cable over 50 feet is assessed a cost per foot for the 6-wire shieled cable. When you order the LBW-420 with the remote sensor, it will come already calibrated with the length of cable specified.