Comment by minkles
Well nothing which is why people are spreading stuff about it being a hack causing the batteries to explode. Which disrupts everything with a network connection and battery. Adds confusion to the situation.
As I said elsewhere this is a one shot attack. They would never be able to pull this off again at this scale.
It's effects might have been intended as much for psychological as lethal results. This specific vector may be a one-and-done tactic but Hezbollah members would be foolhardy not to regard every electronic device that is, at minimum, younger than $pager_age with suspicion. At this point even if it's a wired copper POTS line I'd be asking the intern to take my calls and shout things out from a few rooms away.