Google has unveiled a new project called the Physical Web, which it describes as "an approach to unleash the core super power of the Web: interaction on demand."
What kind of interaction on demand? From the details given, interplay between a smartphone-equipped user and appropriately programmed smart devices. "People should be able to walk up to any smart device -- a vending machine, a poster, a toy, a bus stop, a rental car -- and not have to download an app first [to interact]. Everything should be just a tap away."
The core idea is to create a standard by which smart devices can dispense URLs to other nearby devices. For example, parking meters could provide a URL that links to a tap-to-pay system, or a bus stop could provide a link to an up-to-the-minute route schedule.
The master introduction document for the Physical Web, as provided on the GitHub site for the project, goes into further detail. One key component is that the receipt of anything broadcasted is by default entirely passive. "No proactive notifications," the documentation says. "The user will only see a list of nearby devices when they ask." In theory, someone could write a client that actively notifies users by default, but the idea is to set a good, non-invasive example for potential future developers.
A technical overview of the Physical Web describes how URLs are broadcast to devices via BLE (Bluetooth Low Energy). As currently devised, there isn't much room in the broadcasted packet for the URL itself -- a maximum of 18 bytes -- so a URL shortener or similar service would be needed. A proof-of-concept client, written for Android and iOS, provides the user with a list of nearby devices broadcasting in this fashion, sorted by signal strength.
Scott Jenson, who drafted the overview (and the rest of the Physical Web documentation), notes there may be many ways to broadcast the data. BLE is used in this particular incarnation of Physical Web only because of its ubiquity in mobile devices. "This should not be the only wireless solution," he notes, "but it is the easiest to use at the moment so we can experiment and prototype this system."