The Chirp app plays a 2-second-long noise sounding like a robotic bird that, when heard by another smartphone, triggers a download, the BBC reported Sunday.
Currently the app, developed by Animal Systems, a spinoff from University College London, can send pictures, Web site links or 140-character text messages.
While there are already apps that allow users to swap material via Bluetooth, WiFi or links to cloud-based storage, Chirp can quickly send data to multiple devices at once without them needing to be either paired or have a wireless connection, its developers said.
If recipients are offline their devices will remember the "chirp" and download associated content later, they said.
"We are pretty sure this is unique," the firm's chief executive Patrick Bergel told the BBC.
"It's fairly novel to be able to transmit information to anyone who is in earshot -- a large number of devices can share the same information at the same time using sound," he said.
Chirp's distinctive sound allows it to signal at low volumes in relatively noisy locations such as restaurants or on busy streets, he said.
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