A patent filed by Fitbit has led to the suggestion that the company could be working on a smartwatch device or similar wearable that is capable of tracking the user's mental health or mood. The Fitbit wearable would use non-invasive methods to help diagnose mental state; however, some parts of the patent do set off privacy alarm bells.
https://www.notebookcheck.net/Future-Fitbit-wearable-could-offer-mental-state-monitoring-and-mood-tracking-at-a-potential-privacy-cost.588440.0.html