Detecting threats to public spaces typically requires a multi-layered approach, where different technologies with complementary strengths and weaknesses are combined to create a single screening process. With well-known concepts like “swiss-cheese model” and “defence in depth”, it might seem a no-brainer that more layers of security equals better security. However, a paper recently published by JRC advocates for a more nuanced approach. More layers of detection can potentially result in better security – but it all depends on the layers’ comparative strengths and weakness, and how the results from different layers are combined. The paper concludes that designers of security checkpoints must adopt systems-based thinking, as equipment-based thinking alone is insufficient to properly understanding of the overall performance of a multi-layered screening process.