Upgrade existing wall switches with smart automations - no rewiring or switch replacement - by installing Shelly i4 DC Gen4 behind the switch and powering it with 5-24 V DC. It monitors four dry-contact inputs (SW1–SW4), detects presses, multi-clicks, and holds, then triggers scenes and advanced automations across your smart home via Wi-Fi/Zigbee/Bluetooth/Matter - controlling devices like Shelly 1 Gen4 and Plug Gen4 or calling MQTT/HTTP endpoints.