Our RJ-45 single Dry Contact Sensor is a switch type sensor, so it does not measure voltage, it is either on or off. You can configure this as either an input (normal state is closed GND, or Open/+5V), or an output (set level to either a Low/GND, or a High/+5V). You have to turn off the auto sense feature and configure the sensor (manually)so that this is a relay on the port and not a ?security? sensor, which the units web interface will show after it is plugged in.