BACKGROUND: Outdated communication technologies in healthcare can place patient safety at risk. This study aimed to evaluate implementation of the WhatsApp messaging service within emergency surgical teams. METHODS: A prospective mixed-methods study was conducted in a London hospital. All emergency surgery team members (n = 40) used WhatsApp for communication for 19 weeks. The initiator and receiver of communication were compared for response times and communication types. Safety events were reported using direct quotations. RESULTS: More than 1,100 hours of communication pertaining to 636 patients were recorded, generating 1,495 communication events. The attending initiated the most instruction-giving communication, whereas interns asked the most clinical questions (P < .001). The resident was the speediest responder to communication compared to the intern and attending (P < .001). The participants felt that WhatsApp helped flatten the hierarchy within the team. CONCLUSIONS: WhatsApp represents a safe, efficient communication technology. This study lays the foundations for quality improvement innovations delivered over smartphones.