Well, again, Mossad supposedly claimed that the "explosive was carefully calibrated to injure only the person holding the pager and not harm people standing next to them".
Clearly they were relying on Hezbollah members to not give or sell the (used) compromised devices to outsiders. And if they were monitoring the conversations of each one, they might have been able to even discern occasionally if such a transaction had occurred, and thereby deactivate the applicable device.
The false reports on social media about solar panels, laptop computers, microwave ovens, etc exploding may well have been engineered by Mossad, too. To increase the mass panic and fear that Israel could magically detonate any electronic device.
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