Wearable computer system and modes of operating the system

A wearable computer system has a user interface with at least an audio-only mode of operating, and that is natural in appearance and facilitates natural interactions with the system and the user's surroundings. The wearable computer system may retrieve information from the user's voice or surroundings using a passive user interface. The audio-only user interface for the wearable computer system may include two audio receivers and a single output device, such as a speaker, that provides audio data directly to the user. The two audio receivers may be miniature microphones that collaborate to input audio signals from the user's surroundings while also accurately inputting voice commands from the user. Additionally, the user may enter natural voice commands to the wearable computer system in a manner that blends in with the natural phrases and terminology spoken by the user.