Policing literature has shown how the police deal with protests on the street. This paper aims to add another dimension to this work by focusing on the use of radio‐cell analysis and codes in police tactics to identify and single out protesters. Combining the literature on policing with work on codes and software sorting, the paper shows how an algorithm structures and narrows down large datasets on thousands of protesters into a manageable number of suspects whom officers can investigate using the means they have. The case study involves large‐scale anti‐fascist direct actions and blockades in Dresden, Germany, in 2011 that disabled one of Europe's largest fascist demonstrations. Using this example the paper makes two points. First, the police used the radio‐cell grid to create digital kettles to isolate groups of protesters. Radio cells that overlay spaces in which riots or blockades occur become the boundaries of these digital kettles. Every mobile phone user within one of these spaces is automatically subject to further investigation by the algorithm. Second, the algorithm analyses all phone users within a digital kettle according to movement and call patterns. This way, the code identifies a manageable number of individuals out of hundreds of thousands of connectivity data. As opposed to using officers in riot gear, a radio‐cell analysis and the use of codes enable the ‘kettling’ of far larger numbers of protesters, making this tactic an efficient way of dealing with protests and civil disobedience. Empirically, the paper is based on an analysis of minor interpellations dealing with radio‐cell analysis and semi‐structured interviews with key informants.