From a legal perspective, are there any regulations on these kinds of attacks? Meaning, are they allowed? Are they considered a war crime or maybe this is still a gray area?
It's not that there is a list of approved ways to attack your enemy. Inventing new ways to take enemy by surprise is absolutely a part of warfare. What's important from legal perspective is the ratio between military effect and collateral damage. In this case so far it seems it was better than if conventional warfare was used.
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.
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.
