Hezbollah can't use normal telephones/smartphones/computers to communicate. They know that's just handing over their data to Israel. They use pagers. Pagers work on a broadcast system, so the location of the pager is not communicated back to the cell tower like with a smartphone. For security reasons, you also usually switch pagers and numbers every few months.

A bunch of Hezbollah pagers exploded today. Most of the injuries/casualties were to Hezbollah members, but a few were women and children, presumably family members of a Hezbollah soldier who answered his pager for him.

People believe that Hezbollah made a bulk order/shipment of pagers. Unfortunately for Hezbollah, the shipment was intercepted by Israel/Mossad. Explosives were planted in the pagers, along with a software code to detonate, presumably when a specific text was received. It's unknown if it also contained a bug that recorded and reported conversations.

A normal pager battery doesn't have enough energy to produce that type of explosion. It had to be military-grade explosives. It was incredibly successful, with the target-to-civilian casualty ratio extremely high. There were videos of explosions where the target was injured but a bystander standing next to them was uninjured. The explosion either was in someone's pocket ripping out their insides, or in their hands exploding off their fingers and face. Crippling someone can actually be better than killing them, because now you have a useless mouth to feed, someone who can't fight or work.

Apparently Iran's diplomats in Lebanon had Hezbollah pagers, and were also injured.