Apple began discussing integrating health sensors into future sports-oriented headphones in a patent application that was published back in April 2009 and filed in 2008. Apple's engineers noted at the time that "The sensor can also be other than (or in addition to) an activity sensor, such as a psychological or biometric sensors which could measure temperature, heartbeat, etc. of a user of the monitoring system." After filing a series of patents in 2020-2021 on AirPods with health sensors, earlier this month Apple's Machine Learning (ML) Research team published a technical paper on using specialized health sensors into future AirPods