Truth be told, Alerts aren’t terribly different from the normal chat function, which passes data from phone to phone over an ad-hoc network that doesn’t rely on cellular signals. In the case of alerts, the info will be passed on automatically without the user’s involvement — of course, it would only be used for serious announcements, not sales or promotions. Think Amber Alert, not price alert.
Phones that receive the alerts will store them and retransmit whenever they encounter a device that hasn’t received the information, giving the feature a large time window.
Open Garden, the company behind FireChat and the peer-to-peer communication tech underlying it (and which, incidentally, launched at Disrupt in 2012), will formally announce and demonstrate the Alerts feature at the UN’s World Humanitarian Summit in Istanbul next week.