They left Wi-Fi enabled on their cell phones, which automatically connected to the school network when within range. IT staff then associated the log-ins with individual students - allowing them to be identified and caught. Original article (via Washington Post): "A black principal, four white teens and the ‘senior prank’ that became a hate crime"

URL: https://www.washingtonpost.com/graphics/2019/local/teen-graf...

Makes sense. The home automation platform I use (Home Assistant) can use information from wifi APs for presence detection. I have mine configured with my Unifi controller.