MILEAGE BLOCKER F series detection

[aussiebimmer]

Hi all, 
I had a conversation with one of my customers about mileage blocker the other day. He mentioned to me that he has been using it for nearly 2 years now. He said that he usually unplug before doing regular service with BMW to keep the car under warranty. I was amazed that BMW didn't notice such device has been installed previously. AFASK anything that you plug into the car is recorded in car's data log. What acutually surprised me, those kind of stuff filter the CAN signal and the mileage doesn't change spontaneously after you unplug it. 
 I argued with my customer about BMW can detect any device hooked on the car, even simply simple GPS tracker. Can anyone confirm this info?
Thanks guys

[Fz7]

If you erase the error codes with proper tools BMW can't detect it.

[masa52]

cant detect mileage freezers