The ATSC 3.0 Wake-up feature enables emergency alerts to activate compatible receivers to ensure critical information reaches audiences at risk. Building on next-generation capabilities such as enhanced video, immersive audio, and interactive services, ATSC 3.0 integrates Wake-up signaling through both the Bootstrap layer and the Advanced Emergency Alert Table (AEAT). This paper provides an in-depth examination of the Wake-up mechanism, its technical implementation across the physical and service layers, and its practical implications for broadcasters, device manufacturers, and public safety organizations.