Electronic photoelectric barriers are established devices to time subjects in experiments or athletes in sports. The systems are reliable and precise, but also expensive. We propose a novel, affordable photoelectric barrier system based on consumer grade camera hardware and show how to build such a system with common electronic components and a smartphone. In two experiments with track and field athletes, we show that our novel system has similar accuracy than a professional photoelectric barrier system, but for a fraction of the costs.:1. Introduction 1.1 Motivation 1.2 Commercial Photoelectric Barriers 1.3 Image-based Change Detection 1.4 Existing Camera-based Systems 2. Novel Photoelectric Virtual Barriers System 2.1 Virtual Image-based Photoelectric Barriers 2.2 Mobile Image-based Photoelectric Virtual Barrier System 3. Experiments 4. Conclusion & Future Work