Gesture recognition using the onboard gyroscope and accelerometer (I think - it was 2 years ago!), and it took me some part of an afternoon.

I also used these two resources (the book was definitely useful; less sure if the arduino link the the same one I referred to then), which I found to be useful:

[1] https://docs.arduino.cc/tutorials/nano-33-ble-sense/get-star...

[2] https://www.oreilly.com/library/view/tinyml/9781492052036/

>> Hanson says that while other organizations have similar technology in development, Sony is the first to ship devices to customers.

Following are some links to such similar technology developments for those interested. Of these, [4-5] cover a lot more.

PS: I was the technology lead for [1] below, which I believe is a pioneering work which kickstarted this.

[1] Qualcomm Wants Your Smartphone to Have Energy-Efficient Eyes https://www.technologyreview.com/2017/03/29/243161/qualcomm-...

[2] emza Visual Sense - IoT Visual Sensors https://www.emza-vs.com/

[3] Why the Future of Machine Learning is Tiny https://www.oreilly.com/library/view/tinyml/9781492052036/

[4] The tinyML Summit https://www.tinyml.org/summit/

[5] TinyML: Machine Learning with TensorFlow Lite on Arduino and Ultra-Low-Power Microcontrollers https://www.amazon.com/TinyML-Learning-TensorFlow-Ultra-Low-...