The client will need to run an Update Scan Cycle. If you have absolutely no changes at all; a client will scan weekly.
It will also scan/rescan if the client receives just about any policy change related to updates. I've seen a scan trigger because of the client receiving a software update group deployment policy, a deadline for an already-received software update group deployment policy has passed, CM synchronized and received a policy change for the updates available.
It will also scan more frequently than weekly-by-default if you modify the client agent setting for software update scanning. Personally; because a client scans frequently due to other policy triggers; you can likely leave it at weekly scanning-by-default; because if you update the scan rules by doing a sync for new rules--the clients will re-scan.
Just start looking at some of the default reports for scan results; there are lots of built-in reports for software update scan results.