Maintaining bonds of cohesion between members of small groups in densely populated venues (e.g., a family in an amusement park, or some friends in a stadium) is increasingly gaining interest, both as a safety measure against malicious activity and as a convenient tool to prevent group splitting. Note that the use of mobile phones is often ruled out in such scenarios, due to extreme network load. Current solutions are typically based on custom installations of antennas, centralized control, and user devices with high transmission power.