How to track or get info on someone without them knowing?

Either something you can do through Verizon or with an iPhone or maybe something you can put on their car? Not trying to do anything illegal… My brother is a minor, bipolar and has aspd(sociopathic diagnosed), and has done illegal and dangerous things in the past and it seems like he's starting to again though he swears otherwise. Chances are knowing his history, whatever he's doing will either put him in jail or hurt someone in the very near future. If he finds out she's trying to get info on him he will make it impossible (he is extremely smart when it comes to being shady) any ideas?

That's rather easy if he has a smartphone, there are plenty of applications to do just that, look them up, understand how they work.install them on his phone and use them. Hope i helped =)

If he has a car attach a GPS to it you can find out where he is going as for the phone thing try and listen to his messages that's the only way you will know check numbers