The disclosed computer-implemented method for detecting advertisements displayed to users via user interfaces may include (1) monitoring, via an accessibility API provided by an operating system of the computing device, accessibility events that indicate state transitions in user interfaces of applications running on the computing device, (2) determining, based on an analysis of at least one accessibility event, that an advertisement is being displayed to a user within a user interface of an application running on the computing device, and (3) in response to determining that the advertisement is being displayed, performing at least one action to prevent the advertisement from interfering with interactions between the user and the application. Various other methods, systems, and computer-readable media are also disclosed.