Can you make RFID scanner to detect any 3rd party tags despite countermeasures?

[cave_cat]

suppose Team Red wants to make RFID tags that only their own "authorized" scanners can pick up, such as for tagging merchandise in Walmart. Meanwhile Team Blue wants to be able to find any Team Red tags on items or prove that they are not there. They don't need to extract any info from the tags, only establish their existence and hopefully location.

Who would win, now and in the foreseeable future? Can Team Red achieve "security through obscurity" for their tags? Or can Team Blue detect the presence of the miniature chip antennas regardless of manufacturer's countermeasures?

 

[Tom Anderson]

There could be a type of tag that only responds if it hears a pass phrase. Assuming that Team Blue doesn't have access to the pass phrase, then the tags will not reply to their scanner.

 

[sru2]

They would be detectable because the RFID chip antenna re-radiates energy. Light 'em up and triangulate.