Sleep deprivation is a public health concern that significantly impacts one's well-being and performance. Sleep is an intimate experience, and state-of-the-art sleep monitoring solutions are highly-personalized to individual users. With a motivation to expand sleep monitoring at a large-scale and contribute sleep data to public health understanding, we present WiSleep, a sleep monitoring and analytics platform using smartphone network connections that are passively sensed from WiFi infrastructure. We propose an unsupervised ensemble model of Bayesian change point detection to predict sleep and wake-up times. Then, we validate our approach using ground truth from a user study in campus dormitories and a private home. Our results find WiSleep outperforming established methods for users with irregular sleep patterns while yielding comparable accuracy for regular sleepers with an average 79.5\% accuracy. This is comparable to client-side based methods, albeit utilizing only coarse-grained information. Finally, we show that WiSleep can process data from 20,000 users on a single commodity server, allowing it to scale to large campus populations with low server requirements.