I bet stalking used to be hard. No cell phones, no Internet, things like that. Now a days we even have apps to help you with it. For example, Finding Friends. With this handy app, you can conveniently zero in on the location of your friends whenever you want (though they do have to give you permission at least once).
So I can check on Brea when she's home, Tom when he's working in Chicago, and Jeffrey and Olivia wherever they are (my sister isn't included in that list cause she hangs out with her ex's too much and doesn't want me to know…).