The simultaneous explosion of thousands of pagers used by Lebanese militia Hezbollah on Tuesday was the result of an unprecedented weaponization of a wireless paging system, in which rigged devices detonated upon receiving a coded signal transmitted by radio frequency.

Kelly says first responders and large manufacturers also use pagers. The manufacturers have employees use the devices on factory floors to prevent them from taking photos.

In a period replete with violent attacks across the region—from Israel’s bombardment of the Gaza Strip to the targeted assassinations of militant leaders in Iran and Lebanon—this was perhaps the most sophisticated and daring one yet.

Additional explosions linked to electronic devices caused more deaths and injuries a day after pagers used by Hezbollah exploded, wounding thousands.

Explosions continued Wednesday in Lebanon, killing at least 20 people. The Lebanese government and Hezbollah blame Israel for the apparently coordinated attack. Israel’s defense minister said they are “at the start of a new phase in the war.

The deadly Hezbollah-pager explosions are causing mounting distrust, with some Lebanon residents abandoning their electronic devices.