Remember that a high gain antenna may permit connection or tracking from a distance much farther than specified by the bluetooth spec.

I'm not so much worried about the privacy of bluetooth as I am upset over the high cost of bluetooth to serial adapters. Most bluetooth obd interfaces cost $150 or more. This is at least $50 more than most usb and serial interfaces from the same vendors.

I'd really like carman to support usb so I could build one of these for only $50: http://obddiag.net/products.html