This paper reflects on two funded research projects examining how science and ethics shape the development and deployment of border security technologies in the EU. It examines the different phases of research, development, testing, deployment and maintenance of border security technologies in order to see how different practitioners (e.g. computer engineers; border guards) engage with these material devices. Central to both these studies is the particular way in which the technologies used at border crossings expose broader tensions between mobility and security. I am interested in exploring what that tension reveals about the changing relationships, encounters and negotiations between human and non-human agents. Debbie Lisle is a Reader in International Relations at Queen’s University Belfast. Her current research explores the intersections between travel, culture, security, mobility, visuality, materiality and technology.