alarms, and in this case the active nodes represent the trustable users. But it can also happen that some users could exhibit selfish behavior by disabling the broadcasting functionality, i.e., by acting as passive nodes. Or even some devices could be passive as a consequence of power or bandwidth management. As we do not have any information on the mobile phone users that could let us differentiate them, in our experiment we randomly assign a certain percentage of users as active, and the remaining ones as passive. We then repeat the experiments 50 times, each with a different selection of active users.