Neighbourhood watch messaging groups are part of an already pervasive phenomenon in The Netherlands, despite having only recently emerged. In many neighbourhoods, street signs have been installed to make passers-by aware of active neighbourhood surveillance. In messaging groups (using WhatsApp or similar communication apps), neighbours exchange warnings, concerns, and information about incidents, emergencies, and (allegedly) suspicious situations. These exchanges often lead to neighbours actively protecting and monitoring their streets, sending messages about suspicious activities, and using camera-phones to record events. While citizen-initiated participatory policing practices in the neighbourhood can increase (experiences of) safety and social cohesion, they often default to lateral surveillance, ethnic profiling, risky vigilantism, and distrust towards neighbours and strangers. Whereas the use of messaging apps is central, WhatsApp neighbourhood crime prevention (WNCP) groups are heterogeneous: they vary from independent self-organised policing networks to neighbours working with and alongside community police. As suggested by one of our interviewees, this can lead to citizens “actually doing police work,” which complicates relationships between police and citizens. This paper draws on interviews and focus groups in order to examine participatory policing practices and the responsibilisation of citizens for their neighbourhood safety and security. This exploration of actual practices shows that these often diverge from the intended process and that the blurring of boundaries between police and citizens complicates issues of accountability and normalises suspicion and the responsibilisation of citizens.