Let's get the first thing out of the way - it's not right to fire missiles and rockets at people - as that can cause indiscriminate injuries as well.
Putting explosives in devices such as pagers and walkie talkies - it sounds clever. Just send a signal and an explosion goes off potentially injuring and killing your opponent who has it. It will also disrupt communication methods.
But once you put the explosive in it, you lose control of where it goes and when it gets blown up. It could be a child has it. It could be on a plane - and might not be picked up by security.
You don't know where it ends up. Which means that it has the potential for unintended consequences.
What about any that didn't go off? Are there objects that have been booby trapped and are just potentially waiting to explode - and who knows where they are? The thing about booby traps is that you just don't know who will set them off.
Booby traps seem to be against the International Humanitarian Law if they can injure civillians.
Customary IHL - Rule 80. Booby-Traps (icrc.org)