how is a device recognized in the circle

Hi,

This a pre-buy question from a novice.

I wonder how a device is recognized in the circle? Is it for example by ip or by mac address? Today my child has an iphone and use the private wifi address setting which means that in my current system it is possible to circumvent all my parental settings. Also does the circle also work for wired-devices?

I guess what I am really getting to here ... can I control all devices that my child is using and is it difficult to bypass the controls for a it-savvy child?

Thanks.