The existence of a hidden radio should be trivial to confirm - at minimum it would require a battery and an antenna. If I we're the paranoid type, I'd avoid bl

The existence of a hidden radio should be trivial to confirm - at minimum it would require a battery and an antenna. If I we're the paranoid type, I'd avoid bluetooth security keys all together. NFC should be fine for use with a mobile phone, and while there are attacks that let you read NFC from a few meters away, if you credibly think you have an adversary who can identify you in public, and has this type of specialized hardware, you're dealing with someone who would have a much easier time just throwing you in the back of a van to extract whatever they wanted out of you.