The idea of doing accurate indoor location by placing emitters of 'invisible audio' or audio outside the realm of human hearing in strategic locations within a venue (or outdoors, as one sees fit). Each user may carry a device that is capable of reading these sounds. When the sounds enter the device, they can trigger certain device-specific actions, such as sounds, information or audio. This type of indoor location technology has been explored as an idea by Aaron Parecki but has not been prototyped in the physical sense.
This type of audio-triggered locative technology could also be used passively as one walks through a larger area, such as a city. However, in the case of a city, GPS technology and a passive GPS tracker are better devices for positioning because an invisible boundary such as a shape or geofence can be drawn remotely and easily instead of a physical device, and one's phone entering that space can trigger an action to happen. However, in the case of a city with large buildings, such as New York, the accuracy of GPS has a great chance of having interference, so location based on invisible audio might be feasible, as long as the sounds can be detected above or between the noises of a crowded city.
A different type of audioscape in which one’s mobile device emits certain sounds ambiently or when triggered by the user. Most notably, the application Audio Perfume for iPhone, created by [Jason “Fekaylius” Wilson] enables users to be ‘adorned’ with all sorts of different sounds, even while the phone is asleep. These sounds, one of them the sounds of multiple camera clicking rapidly, invoke certain effects in those who hear them. In the case of the camera clicks, those in one’s vicinity suddenly feel as if they are paparazzi and subsequently look for the source of the noise.