A Simple Interface (SI) is an interface between devices and a home network in the Home Electronic System (HES). The SI type 1 connects simple devices offering and accepting only a two state signal to an HES home network. Two signals are available at the SI type 1. One is a control signal for turning the device on and off. The other is a monitor signal for checking the state of the device. This part of ISO/IEC 10192 specifies the mechanical, electrical, functional and procedural characteristics of a specific Simple Interface (SI). The SI type 1 is a physical interface realized between the SI type 1 device and the SI type 1 Network Access Unit, NAU. It also serves as a reference point.