There are three basic types of WBICs: stand-alone controllers, add-on devices, and plug-in devices. All three types of WBICs are available in a variety of sizes appropriate for small residential and large commercial applications. Add-on and plug-in devices connect to standard clock timer controllers and modify their irrigation schedule. Light commercial products often have the same features as the residential products, but with greater station capacity. Computerized central control systems are typically used for large properties, such as parks, school districts, and golf courses, and are not discussed in this fact sheet.
There are two primary technologies employed by WBICs: onsite sensor-based control and signal-based control. Onsite sensor-based controllers use real-time measurements of locally measured factors (e.g., temperature, humidity, solar radiation) to adjust irrigation scheduling. An onsite sensor-based system may have historic weather information for the site programmed into memory, which it can use to modify the expected irrigation requirement for the day or calculate onsite evapotranspiration (ET) for the landscape. In contrast, signal-based controllers receive a regular signal of prevailing weather conditions via radio, telephone, cable, cellular, Web, or pager technology. The signal typically uses data from local weather station(s) to update the current schedule for the controller.
Source: Weather-Based Irrigation Controller Mini Report (https://www.epa.gov/sites/production/files/2017-01/documents/ws-products-minireport-irrigation-controllers.pdf)