A group of students at Carnegie Mellon University have created Acoustic Barcodes: a series of etched lines placed on almost any surface that is read by a system via the unique audible waveform given off when an object - like a fingernail or pen - is ran across the notches.
The team led by Chris Harrison, a PhD candidate in the Human-Computer Interaction Institute, used a simple contact mic to attach a binary ID to a number of materials including glass, stone, wood and metal, providing another inexpensive way of adding digital interaction into the real world alongside the likes of NFC and QR codes. The video below demonstrates a few potential applications of this technology, including initiating a file sync on your smartphone by dragging the device across a code (although we wouldn't really want to scuff our phone like that), use in school as a set of widgets, or on shop windows to give descriptions of the products on display. Beyond these presented situations, comes an altogether bigger usage possibility to those who are vision impaired: acting almost like a secondary aid to Braille, adding extra detail to the world around.
Source: Chris Harrison