Comment by ebcode
If the pagers had been equipped with lasers that caused blindness, there is a Geneva Convention protocol going back to 1995[0].
I would like to think that the spirit behind that protocol is that the intent to cause permanent blindness in your opponent should be considered a crime. And not that it's not a crime so long as you don't use a laser to do it.
So you can put me in the camp of "this should be considered a war crime", even if it's not in any books yet.
[0] https://en.wikipedia.org/wiki/Convention_on_Certain_Conventi...
If the pager was sent a message that would encourage the soldier to bring the pager to their face, it would certainly fall under an intentionally blinding attack.