Last November, as part of an investigative series on Apple's meetings with the FDA, we reported the company's stated plans to develop "two possible (and related) products in the cardiac space" which would require FDA clearance. In that report we speculated, based largely on a quote from Tim Cook in the Telegraph, that one of the products might be a wearable ECG built into an Apple Watch strap, similar to Kardia's mobile ECG offering.

"We don’t want to put the Watch through the Food and Drug Administration (FDA) process,” Cook told the Telegraph. “I wouldn’t mind putting something adjacent to the watch through it, but not the watch, because it would hold us back from innovating too much, the cycles are too long. But you can begin to envision other things that might be adjacent to it -- maybe an app, maybe something else.”

But there's another strong contender for something adjacent to the watch -- or, as the case may be, adjacent to the phone: headphones. And there's actually evidence that Apple has been investigating heart-monitoring earbuds for at least three years.

Apple patented health-sensing earbuds back in 2014 and Mac Rumors reported in November that the company filed an update of that patent with language that clearly refers to AirPods, the wireless ear buds Apple announced alongside the iPhone 7, meant to soften the blow of the much-maligned removal of the headphone jack. 

A few months after the original patent, a source on now-defunct gossip app Secret -- who had previously leaked Nike's plans to shut down its Fuelband division, lending them some measure of credibility -- said a health sensor would be built into the next generation of Apple's earbuds. This obviously never came to fruition.

In addition, there's Valencell's patent lawsuit against Apple, which was filed a year ago and is close to closing its discovery period. While the patents at issue in the case deal with wrist-worn heart rate sensors, Valencell is known for building heart rate sensors into its earphones and the whitepapers that the company accuses Apple of accessing under false pretenses include one called "Earbud-Based Sensor for the Assessment of Energy Expenditure, Heart Rate, and VO2 max”.

Obviously a few rumors and patents over the years don't add up to a statement of fact, but it's a number of rare glimpses into Apple that all point to the same conclusion: the company has been interested in ear-based heart rate monitoring in the past. With so much riding on the success of AirPods to justify Apple's decision to nix the headphone jack, it would be a strong way to make future generations of the peripheral more enticing.