Described herein are several embodiments relating to irrigation controllers. In many implementations, the irrigation controllers includes a housing; a control unit within the housing and comprising a first microcontroller configured to execute stored irrigation programs, wherein the control unit includes an interface connector port; a driver circuitry within the housing configured to actuate irrigation valves based on control signals received from the first microcontroller; and a removable plug-in device removably coupled to the interface connector port, the removable plug-in device comprising a second microcontroller configured to send and receive data communications to and from the first microcontroller, such that the first microcontroller and the second microcontroller function together during use of the irrigation controller, wherein the removable plug-in device does not include any driver circuitry configured to actuate any irrigation valves based on any control signals received from the first microcontroller.