Oregon Scientific THGN123N Ultra Cold Temp/Humidity Sensor Wireless remote indoor/outdoor temp/humidity sensor for some OS weather stations Operates in temps down to -40 degrees F; transmits on 1 of 3 different receiver channels Transmits data from up to 100 feet from the main unit (various units sold separately) Requires 2 AAA lithium batteries to work in ultra-cold setting conditions Check Oregon Scientifics Website for compatibility with your OS weather station