The chapter presents and analyses forms of presence detection in the control of border transgressions by using sonar and haptic technologies that ‘listen’ to and ‘feel’ for presences and hidden persons, and different forms of imagery, notably radar and infrared. Such technologies do not identify individuals but only kinds of bodies - humans, birds, donkeys. The border guards develop refined skills for distinguishing the living from the inert, humans from non-humans. The chapter pursues by inversing the perspective to encompass different forms of surveillance of the surveyors themselves, whether by migrants or management, with a vivid description of migrant technological skills and tactics for crossing the border.