This is kind of neat. MIT has a test for antibodies (so it would test positive for either vaccinated or recent infection) that only takes around 10 minutes.
It does require a drop of blood, so unfortunately it's probably not something that people will be doing outside sporting events to test for who can be let in, but more options are better than no options.
https://news.mit.edu/2021/smart-deve...-immunity-1122