This article explores the functioning of citizen security. It is developed with reference to the initiatives in Tijuana, Mexico, and reveals how citizen security operates through technologies that simultaneously generate both compatible citizens and abject non-citizens. Both groups become an integral part of citizen security and operate within a logic through which one tries to ensure the life of the former (biopolitics) and the exclusion of the latter is generated (the necropolitics). From biopolitics, the population is understood through surveillance measures that allow the accumulation of information and the analysis of data. These concern the observed patterns of behavior within this population, with the aim of managing random events and populations outside of what is empirically normal. These abnormal populations are then regulated through initiatives composed of the National Program for the Prevention of Crime (PRONAPRED), with the purpose of giving them certain life skills to overcome their risk situations. On the other hand, non-citizens are treated based on an exclusionary inclusion (the necropolitics). In practice, this implies that the non-citizen population is seen as an object of hierarchical surveillance. The latter is designed to regulate movement and limit the danger that these non-citizens represent for public safety. Similarly, non-citizen individuals are marginalized to the extent that their inclusion in the PRONAPRED security programs makes possible their eventual expulsion from Mexico. Thus, the article concludes that citizen security determines and exacerbates the citizen / non-citizen distinction, a distinction that can mean life or death.