Just plug the thermometer/hygrometer sensor into the headphone port on: iPod Touch (4th gen or later), iPhone 4 (or later), iPad (2nd gen or later) or iPad Mini (or later) to measure the ambient air temperature or current humidity level. Download the free app to access all features: HI or LO values, graph display, programmable alarm values, dew point, photo & log function, and share/print function. No battery requirement.