It was not immediately clear how those devices were distributed, but large numbers of pagers exploded at approximately the same time on Tuesday in Lebanon, causing thousands of injuries, according to Lebanese health authorities.

Since the advent of cellphones and smartphones, pagers have fallen out of use, though they remain in use by some people for quick and private contact.

Hezbollah has been security-conscious about telecommunications for years, Al Sabaileh said, and has long banned its operatives from using cellphones while they are traveling in the south of the country near the Israel border. Cellphones can be used to locate the person carrying them.

But, he said, that became more urgent after Oct. 7, when some of the Hezbollah's senior members were assassinated in airstrikes. In February, Hezbollah's chief, Hassan Nasrallah, warned members during a speech that their phones were dangerous and could be spied on by Israeli forces, saying they should break or bury them.

Iran, whose government has for decades supplied Hezbollah with arms, technology, and other forms of military aid, would have been pivotal both to any decision to switch to the system and in the delivery of the technology, the experts said.

Experts said that they did not know the precise arrangement for the distribution of the paging devices to Hezbollah members, nor how the devices had been compromised, but a key element of the new paging system was that it did not use the technology that is the basis of most conventional cellphone networks, and therefore, the devices were harder to track electronically.

David Wood, a senior Lebanon analyst with the International Crisis Group think tank, described it as a "limited, closed network."

He said that in the short term, Hezbollah would likely resort to other methods of communication, potentially one that avoided electronic means altogether.

"It will obviously make coordination more difficult and more risky, and without a doubt, this is a serious blow to Hezbollah's operational capacity," he said.

Al Sabaileh said the explosions would be a psychological blow for Hezbollah because it showed the capacity of Israel to strike not just fighters but anyone connected with the group as they went about their daily business.