He had seen her leave this big box out front, and he knew that he was going to have a chance that he might not get again. At this point even if she would catch sight of him she would not know who he was. As long as she didn't see him messing with her box, then she should not be any the wiser. He waited for her to be out of sight before he approached. He watched to make sure that no one was around or even looking at him.
He walked nonchalantly to the box, and then when he was right beside it he bent to check his shoes and slid the tracker into the edge of the box. Once that was done he simply stood back up and walked down the street, but kept within eyeshot. He wanted to make sure that she didn't discover it. He knew if she found it she would know that someone was after where she was going.