Computer engineer Josiah Hester is outside a Latin American street food restaurant in Evanston, Illinois, with four of his computer science graduate students, talking above the rumble of an El train as it passes overhead, sweating in his Hawaiian shirt, and waiting for the bag of burritos he’s bought them. As they wait, he quizzes the students about ShotSpotter, the controversial tech company that the city of Chicago hired to monitor violence on the city’s South Side with hidden microphones that locate gunshots via triangulation.