Attributes . Contains External Temperature and Humidity Sensors, All EnviroTrak 900 MHz Transmitters Operate In A 900 MHz Frequency-Hopping Spread Spectrum and Reach Up to 2500 ft., Open Field Range, Interior Range Up to 500 ft., The 900 MHz System is Capable of Collecting, Storing and Transmitting Data Wirelessly Up to 400 hr., Battery Operated . Names