The Honeywell C7189R1004 is the correct accessory part for the following:
The Honeywell Wireless Indoor Sensor monitors the humidity and temperature that transmits it wirelessly to your thermostat. Also known as part number C7189R1004, this Honeywell Indoor Sensor can be used to change the sensing location of the thermostat. You can use up to 6 Honeywell Wireless Indoor Sensors per thermostat. This sensor works with RedLINK 2.0 thermostats and can sense temperature and humidity remotely.
Honeywell Wireless Indoor Sensor specifications:
If you install multiple sensors, the thermostat can monitor temperature and humidity in separate locations. You can set it to monitor different readings from different sensors. In this case, one sensor can control humidification in one area, while another sensor can control dehumidification in another area of your home.