The enabling area is the region where the emergency takes place and where people are close enough to be aware that an emergency is occurring without the need to receive any message. As a consequence, alarm messages are originated by the active devices that, at a certain time, are located in this area, namely the enabling devices. Clearly, all the active devices contribute to diffusing the alarm by moving and by re-broadcasting a received alarm message, but only the enabling ones are allowed to start the spreading.