There's literally a switch inside the phone for this, you can detect it being hooked from its actual plug. The elegance from using the phones own hardware is mi

There's literally a switch inside the phone for this, you can detect it being hooked from its actual plug. The elegance from using the phones own hardware is missed in mindlessly bolting on another sensor, leaving the phone nothing but a shell, this detracts so much from the otherwise neat idea of "having a physical device restrict your internet connection."