Smart switch devices, systems, and methods for modifying an existing electrical system to utilize the power state output of a physical switch as an indicator or signal for the operation of a smart home device or system or network of such devices to facilitate interoperability of physical switches with smart devices. The smart switch detects or determines the power state of a circuit and infers the corresponding state of a mechanical switch that operates the circuit. This information is then transmitted to associated smart devices, which may not be physically connected to the circuit controlled by the switch. When the mechanical switch is operated, it can control both electrically attached loads, such as a conventional light or appliance, and wirelessly control unconnected smart devices.