A smart ring is a ring, worn on a finger, that contains sensors, a tiny battery and a radio chip. It tracks sleep, heart rate and activity day and night. Some smart rings can also pay at a shop counter with a tap. A smart ring weighs only a few grams, and a start-up in Bengaluru is among the companies that make one.
The ring measures the body with three kinds of sensor chips. The first is an optical sensor. Small lights shine into the skin, and a light detector measures how much light comes back. Blood absorbs light, and the amount of blood under the skin changes with every heartbeat. So the reflected light rises and falls with the pulse, and the ring can work out the heart rate. The same sensor can estimate the oxygen level in the blood. The second sensor is an accelerometer, which measures movement, so the ring can count steps and tell when the wearer is still. The third measures skin temperature. The finger has many blood vessels close to the surface, and a ring fits closely, so the readings are steady, especially at night. The battery lasts about four to seven days between charges.
The ring is one part of a three-layer system, described on IoT architecture. Firmware on the ring's own chip reads the sensors and stores a summary. When the phone is nearby, an IoT wireless chip in the ring sends the summary to the phone app over Bluetooth Low Energy, a version of Bluetooth that uses very little power. The maker's servers then analyse the data and send results back to the app.
Consider a nurse in Kochi who works night shifts and wants to know whether she sleeps enough during the day. After one shift, the ring records that she fell asleep at 9:40 a.m. and slept 5 hours and 10 minutes, with a resting heart rate of 62 beats a minute. When she opens the app in the afternoon, the readings reach her phone, and the app shows her sleep score. Over a month, the app shows that she sleeps least after the third night shift in a row.
A smart ring is a wellness device, not a medical device. Its readings are estimates, and they are not a diagnosis. Patients whom doctors watch closely at home wear medical devices instead, such as remote patient monitoring wearables or Holter monitors, which record the heart's electrical signals. The page on remote patient monitoring explains how doctors use such data.
Some rings can also pay by tap. A small payment chip inside the ring holds a token, a different number that represents the owner's bank card, so the real card number is never stored on the ring. At a shop, the owner holds the ring near the POS terminal, the card machine on the counter, just as they would tap a card. Under the RBI's rules, small tap payments of up to ₹5,000 need no PIN.