I am just out of the gate, but the videos show sharp percussive explosions and no lithium evidence. So C4 or RDX in the devices on a 'mod board' with the explosive disguised as a big capacitor or something. It had to be put into the devices. In order to justify an operation like this the explosions had to be near-simultaneous so the mod board had to have its own clock, which would be as accurate as the crystal in the clock circuit provides, maybe drift of +/- a few seconds since installation.
The broadcast pager network does not offer this level of time precision for a detonation message so as ugly as it sounds, I believe at the moment that 9/17/2024@3:30pm (or whatever) was preloaded into the 'mod boards'.
Perhaps the 'mod board' had the capability for the future time to be set with a broadcast message, but that introduces such complexity! It requires the page system itself to be compromised. The victims' paranoia served them badly in this case, a recent warning about cell devices and a lower tech 'solution' is rolled out and they would only trust one source, so all you'd have to do was get an explody batch into the supply chain with (reasonable) assurance that only Hezbollah members would get them.
In the coming days I'd look for clues in: The simultaneity of the explosions with times to the second // were any duds found and disassembled? // is there a separate radio receiver on the mod board (to set future detonation time) // when did the 'rollout' of the devices begin? // How many pager carrying non-members were injured and what were the circumstances ('medics' being one group) // Will suspicious broadcasts be discovered from logs or logged radio intercepts?
Given the people we are dealing with (I mean both sides) I am thinking that the operation avoided ANY covert channels at all and was a simple date-time bomb.