The main feature of a smart assistant device is its ability to provide voice recognition and natural language processing capabilities. These devices, such as Amazon's Alexa or Google Assistant, can perform a variety of tasks, including answering questions, controlling smart home devices, and providing reminders. By leveraging AI, smart assistants facilitate hands-free operation, making technology more accessible and user-friendly. This feature enhances daily convenience, allowing users to multitask effectively while relying on voice-activated commands for assistance.