Because of all the moving parts and the interaction with software, the field performance issues that arise will depend on a number of factors. If the intent is to alert authorities that a person wearing a GPS tracking bracelet has entered a zone he should not be in, a simple oversight in configuring that zone could mean that the person wearing the ankle bracelet, taking public transit and going along the usual route that they take, could cross into a zone without even being aware of it.
They have no control over that. The training involved in properly setting up a GPS tracking program is considerable. The officers are well trained to define their zones carefully. They avoid setting up zones where their client would be expected to travel. If we're trying to limit entry or we want to be alerted of entry into a park or school, if you make your zone three or four times the size of that park or school, and if the person is travelling through that area, it is very easy to generate an alarm even though he did not enter the park or the school itself.