Disclosed are various embodiments for decoding an audio signal to identify information encoded in a human-imperceptible portion of the audio signal. A client device may capture an audio signal broadcast wirelessly from a transmitting device. A human-imperceptible portion of the audio signal may be decoded to access at least one unique identifier encoded within the audio signal. A request for at least one notification may be sent to a notification service over a network, where the request includes the at least one unique identifier and data associated with the client device. The remote service provides the client device with a notification to render in a display.