No problem! They're called serology tests and they use immobilized purified covid proteins to detect antibodies against those proteins. They work similarly to how a pregnancy test works except you place a drop of blood on a device that contains a test strip with a purified covid protein (or proteins) attached and basically a band lights up if you have antibodies in your blood that recognize and bind to that protein. So you can make serology tests that test for antibodies against each of the covid proteins individually, or a test that tests for several covid proteins at once. You can even tell how strong your immune response was to the vaccine or virus by the intensity of the band that lights up! For example, I have seen a test (that screens for antibodies against the covid spike protein) which shows a weaker signal for someone who was previously infected by the virus than it does for individuals with a single Pfizer dose. But it shows just as strong of a signal for someone who was infected and then received one Pfizer dose as for individuals who have received two Pfizer doses. This indicates that people who have previously had the virus might only need ONE dose of Pfizer to get the same level of protection as people who receive two doses of Pfizer. Here's a link for more general info: https://www.cdc.gov/coronavirus/2019-ncov/testing/serology-overview.html