A resource server system granting to users access to a resource based on the very fact that the users' computing systems can demonstrate that they heard an audio signal. Specifically, the resource server system detects receipt of a message from a client computing system, and interprets the message as representing that the client computing system heard an audio signal. In response, the resource server system grants a user of the client computing system access to the resource. This may be performed for multiple client computing systems that each demonstrate that they heard the audio signal. Thus, the principles described herein allow for the granting of access to resources to other computing systems within the audible proximity of a computing system that transmitted the audio signal.