Intrusive harvesting.
"Today the US Patent & Trademark Office published a patent application from Apple that relates to a next-generation of AirPods Sensor System wherein the housing and tips of AirPods could include a number of active and reference electrodes configured to measure biosignals and electrical activity of a user's brain. The biosignals measured by AirPods could include, but are not limited to, an electroencephalography (EEG), electromyography (EMG), electrooculography (EOG) and more.
In Apple's patent background they note that brain activity can be monitored using electrodes placed on the scalp of a user. The electrodes may in some cases be placed inside or around the outer ear of the user.
Measuring of the brain activity using electrodes placed in or around the outer ear may be preferred due to benefits such as reduced device mobility and decreased visibility of the electrodes when compared to other devices that require electrodes to be placed on visible areas around the scalp of the user."