A Washington Post investigation on Hezbollah's pager explosion attack has revealed:

The devices had the ability to transmit encrypted messages, but it was necessary to press two different buttons at the same time to read them - thus Israel ensured that they would be in the hands of Hezbollah personnel at the moment of the explosion. 

Israel provided Hezbollah with pager devices as early as 2015, and they had an especially large battery that allowed Israel to eavesdrop on Hezbollah's communications for the last nine years.