I've been using a legitimate app called Porofessor that provides a lot of helpful info when playing league of legends, such as displaying objective / jungle camp timers when things will respawn (such as dragon, baron, jungle camps etc), showing player histories like champ statistics, win rates, etc, and also suggests runes and can auto-fill them into your slots to make it easier to prep for a match.
The jungle timers in the app will go off for camps the player doesn't have vision of, for example often times i'll see a camp on the opponents side suddenly show a timer, and will realize that their jg must have just cleared it and is in that location, even though i've got no vision there.
Update - I was wrong; apparently it was showing them when a camp was about to respawn, at 60's , not when it was just killed. So I would be recognizing that the JG should be there soon rather than just cleared it. Coincidence