In a first speech detection mode, a computing device listens for speech that corresponds to one of a plurality of activation phrases or “hotwords” that cause the computing device to recognize further speech input in a second speech detection mode. Each activation phrase is associated with a respective application. During the first speech detection mode, the computing device compares detected speech to the activation phrases to identify any potential matches. In response to identifying a matching activation phrase with a sufficiently high confidence, the computing device invokes the application associated with the matching activation phrase and enters the second speech detection mode. In the second speech detection mode, the computing device listens for speech input related to the invoked application.