Oregon Scientific THGR800 Thermometer & Humidty Sensor with 3 Transmission Channels Wireless remote indoor/outdoor temp/humidity sensor for some OS weather stations For use with Oregon Scientific WMR90A, WMR100, WMR100N and WMR200 stations Operates in temps down to -58 degrees F; transmits on 1 of 3 different receiver channels Transmits accurate data from up to 100 feet from the main unit (sold separately) Requires 2 AAA lithium batteries to work in ultra-cold setting conditions