Passive tags are unpowered data storage methods designed to be machine-readable. The most successful implementation of passive tagging, by far, is the barcode. Other passive tagging systems include QR codes and NFC chips. Those both work well, but require specific hardware: a camera for the QR codes and a reader for the NFC chips. Asterisk and Obelisk are new passive tagging methods that can be easily integrated into modern smartwatches and rings without additional hardware.
Even the least expensive smartwathes and fitness trackers have a built-in IMU (inertial measurement unit). That IMU is how they’re able to track your steps. Integrating a camera, along with the requisite processing power, to scan QR codes would add a non-trivial amount to the build cost. NFC readers, while they’re not expensive, would add to that cost as well. The Asterisk and Obelisk passive tags, developed by researchers from the University of Toronto and University of Waterloo, wouldn’t add any cost to standard wearables because they utilize the IMU that’s already present.
Both types of tags are “read” when the user traces their finger over a pattern. The Asterisk pattern is a star shape, and the Obelisk pattern is a more free form series of connected line segments. Both can be printed on any sheet of paper with normal methods. As the user tracers the pattern, the IMU picks up the movements to decipher that pattern. It can then pull up a website, place an entry on the user’s calendar, or add contact information — just like a QR code.