Smartphones keep us awake, but do they harm all age groups equally? Drawing on time-displacement and cognitive-arousal theory, we link late-night screen minutes, location of use, and device tier to lost sleep. An industry partner supplied six hundred million app-usage records from thirty thousand U.S. users collected between 2018 and 2025. We turn these logs into daily measures of engagement and attention fragmentation, test our ideas with multilevel and structural-equation models, and double-check them with a deep-learning forecast. A pilot month with forty-five users already shows the slope that Gen Z and Millennials lose the most sleep as midnight use rises, whereas Gen X and Boomers do not. The findings reveal a “dark side” of the attention economy that hits younger generations hardest and highlight design and policy levers for healthier digital habits.