Criminal justice authorities may wish to monitor or to control the location of particular person without resorting to imprisonment. An electronic monitoring device provides pretrial services, probation, or parole the chance to closely supervise convicted person by keeping track of where person are at or in some cases, determine if convicted person is consuming prohibited substances like alcohol or narcotics. Some systems provide tracing within predefined restricted areas. Systems like this are in use for different situations, for example before a criminal trial or after conviction. Authors described different ankle monitor systems that are in use, their advantages, disadvantages and data that collects. For each convicted person data from electronic monitor device is very important. Authors described machine learning method, which based on data could predict whether the convicted person will repeat the criminal offense or not. Methods like this works with hypothesis and gradient descent. At the end authors explored the role of these devices by the law of enforcement sanctions and measures outside the prison.