This paper presents a seamless wireless extension approach to a KNX-based home automation system. The system consists of gateway and switch units specifically designed for this purpose. The gateway acts as the coordinator of the wireless network and a bridge between wireless and KNX networks. Switch units can be operated by a power outlet or battery. With the proposed architecture, it is possible to extend functionality of the KNX to wireless nodes, which consume very low power when they are operated by battery. Experimental results show that a simple yet efficient wireless extension to the KNX system is possible by the proposed system, which also enables more than 5 years of continuous operation for battery-powered switch units.