That's how it would work. The bracelet triggers an alarm as soon as the person is within, let's say, a kilometre from the victim. The victim gets a warning and the police get one too. They know when they hear an alarm that he's inside the perimeter. A police officer will track him down.
At the same time, it gives us evidence for the courtroom. When I go to court with a victim, we never have any evidence. The victim says that the individual was there, but there is no evidence, because the victim didn't have time to activate her cell phone because she had to get away. So the bracelet provides evidence for the courtroom. The police can come and testify that the victim was followed to her place of work, for example. That gives us the evidence needed to incriminate the perpetrator and prevent a murder.
I personally would have liked to be able to go and hide. If the detection perimeter is set at one kilometre, then when the alarm goes off, the victim has time to go to a neighbour for help.