The huge wave of pagers/beepers exploding in Lebanon and Syria yesterday, very probably by Israel, can be called a major war crime or an act of mass-terrorism, but it certainly seems to me that it can not be considered as compliant with the laws of war.
Rule 15. In the conduct of military operations, constant care must be taken to spare the civilian population, civilians and civilian objects. All feasible precautions must be taken to avoid, and in any event to minimize, incidental loss of civilian life, injury to civilians and damage to civilian objects.
https://ihl-databases.icrc.org/en/customary-ihl/v1/rule15
Rule 71. The use of weapons which are by nature indiscriminate is prohibited
https://ihl-databases.icrc.org/en/customary-ihl/v1/rule71
Rule 19. Each party to the conflict must do everything feasible to cancel or suspend an attack if it becomes apparent that [...] the attack may be expected to cause incidental loss of civilian life, injury to civilians [...] which would be excessive in relation to the concrete and direct military advantage anticipated
https://ihl-databases.icrc.org/en/customary-ihl/v1/rule19
Note that those "rules" are summaries of all customary international humanitarian law (non-voluntary global laws of war) by ICRC, responsible for maintenance of e.g. Geneva Conventions, while the underlying conventions and practices are cited on each page for further reference.