Feeling off? Circular’s Immunity Index might explain why

Circular has added something new to its app. The Immunity Index is a health tracking feature designed to flag early signs that your body might be about to get sick.

What the Immunity Index is aiming to do

This is not another stress score or sleep quality metric. But its not entirely new either – we’ve seen similar features on the RingConn and Oura.

Circular’s Immunity Index draws from several data points already tracked by the company’s smart ring range. This includes things like resting heart rate, heart rate variability, breathing regularity during sleep, along with temperature fluctuations. What the company has done is bring them all together into a single, easy-to-read indicator of immune resilience.

Essential reading: Top fitness trackers and health gadgets

The result is a simple score from 0 to 8, color-coded and shown on a card in the app. The number tells you how ready your body is to handle external stress or infection. At the top end, 8/8 means you’re all clear. On the lower end, a 0 or 2 indicates a sharp deviation in multiple metrics that could point to rising inflammation, fatigue or a brewing illness.

The score updates daily, and the idea is that you get just enough information to act early. If you’re slipping from an 8 to a 6, it might be a sign to ease up on intense workouts or prioritise sleep. If you’re at 4 or below, the app encourages taking real rest seriously and includes recommendations that align with that. Simple and to the point.

Who gets it and when

The Immunity Index is now rolling out as part of a standard app update for all existing smart ring users. As long as you’re using the Circular app with the latest firmware, you’ll be able to access the feature and start tracking your daily immunity score right away. For new customers of the Circular Ring 2, it will be part of the setup process.

There are no major settings to tweak or calibration required. The ring already collects the necessary data overnight. All the new feature does is pull those signals into one place and give you a heads-up if something seems off.

The company has started mass manufacturing the second generation ring following a successful Kickstarter campaign that raised nearly $4 million. The sizing kids have been sent out and the shipping process to early backers has kicked off. As compared to the first generation, this one adds ECG monitoring and comes with a fresh new design.

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