What is the default data encoded in the Bar Code / QR Code?
It contains a single number: 42. At least on all the civicrm installation that have a "DON'T PANIC" on the cover

On the others it's contact id + participant id + url to the participant view in your civicrm

There is a hook to alter what's encoded in the QRcode alterBarcode that you can implement from an extension and put something else (eg the name of the participant in clear)

Beware that there is a limit of how much text that you can put in a QR. Last time I checked, the proper way of formatting the content (eg. vcard if you want to put the contact details) so it was understood by all smartphones was a bit of a hit and miss.

Would be great you update us on the state of the art and what works or doesn't