The trick is in opening the app and knocking. The knock releases the advertisement. Similarly, in other use cases, geofencing from the phone means the phone has

The trick is in opening the app and knocking. The knock releases the advertisement. Similarly, in other use cases, geofencing from the phone means the phone has to think it's nearby to release the signal. Not saying it can't happen, but that's a lot of work. Easier to just hack the device, prompt the user with a fake pin-pad or login screen, or do social engineering and/or gain physical access. By the way, this attack is much more successful in reverse, for listening to and replaying keycard transactions. I was shocked to discover how little materials would be needed to make a decent amplified antenna.