So apparently in addition to the hard updates which usually trigger an email/text alert, there are also soft updates as a case progresses through different stages, which don't do anything. They'll have the most recent update on the case and a code to indicate where the case is at. For this trick to work you MUST BE logged into your USCIS account, and I think it only works with cases that start with IOE and some other types of applications.
1. Log in to your USCIS account.
2. In a separate tab, copy/paste the following URL: https://my.uscis.gov/account/case-service/api/cases/yourIOEcase#here
3. Use control + f to look for "updatedat". The topmost "updatedat" will contain the most recent update date, either soft or hard.
4. Use control + f to look for "eventcode". The topmost "eventcode" will contain the most recent "stage".
5. Link to code descriptions.
In my case, my code is FTA0: "database checks received," which apparently means my background check was completed and returned.