The injection of emerging technologies into policing implies that policing mandates in law may become mediated and applied through opaque machine learning algorithms, artificial intelligence, or surveillance tools – contributing to a form of ‘black box policing’ challenging foreseeability and clarity and expanding discretionary legal spaces. In this paper, this issue is explored from a constitutional and rule of law perspective, using the requirements of qualitative legality elaborated by the European Court of Human Rights and the implicit democratic values that they serve. Placing this concept of legality into a wider theoretical framework allows legality to be translated into a context of emerging technology to maintain the connections between rule of law, democracy, and individual autonomy.