Most Helpful Guy
This sounds super healthy, and not terrifying at all!
Most Helpful Girl
Speaking from experience where a guy actually did this to me with my computer, webtracking my every move - it's the biggest insult and so violating to have to learn that this happened. And in my case so unnecessary since I had boring online habits and I also told him I was breaking up with him because he was already smothering and possessive over me.
If you are find out, and you would be because chances are you'll confront him with something about his phone and eventually it would come out that you're tracking him, it can mean a lot of trouble for you to try and explain yourself about. If you're worried about him cheating, worry about it without the phone tracking. If you're just plain worried in general, figure out why because it has nothing to do with him, and he doesn't deserve to be watched like a toddler that you're babysitting.
Anyway, if you really wanted to know about phone jailbreaking, you can Google it. I don't know much about it but it's nothing he also can't get off his phone by simply resetting it too. Sounds like there is more going on that has nothing to do with the actual wish to track. It sounds like you need to have a conversation with the person instead about why you feel this way.1