Check the listing for details. BALDR Wireless Weather Station Outdoor Sensor. Condition: New. Listed at 12.95 USD. This remote sensor is designed to pair BALDR weather stations (sold separately) to expand to three channels to collect data from three different locations. It monitors outdoor temperature and humidity and syncs the data to Baldr Weather Station within a few minutes after powered by 2 AA batteries. It is weatherproof and can be self-standing or wall hanging. Each sensor can lock one channel, and most BALDR weather Stations can add up to three sensors to monitor 3 locations simultaneously. Although it is water/weatherproof, we strongly suggest placing it under a cover to avoid direct sunlight and water exposure to extend product life & provide the most accurate weather data. Please note: after change batteries, if the sensor doesn't sync to the weather station, press & hold the "CH" button on the central station for 3 seconds and release. It serves as forced re-registration, and the two units will pair in a minute or two.