I've been to many (tech-focused, admittedly) conferences that handle this through RFID tags or simple barcodes embedded in the conference badges, the advantage

I've been to many (tech-focused, admittedly) conferences that handle this through RFID tags or simple barcodes embedded in the conference badges, the advantage to that system being that attendees don't have to do anything more complicated than hold up their badge to a badge-scanning attendant. I feel like there's a fantastic use case for the parent's project; I'm not quite sure what it is yet.