A job of mine involved building prototypes for Wear OS. Based on that I'd guess that the idea is at least explorable. Smartwatches do have the needed sensors,

A job of mine involved building prototypes for Wear OS. Based on that I'd guess that the idea is at least explorable. Smartwatches do have the needed sensors, I think. The watch is in a specific position when you touch your face. That should be detectable. There is an API to read them, https://developer.android.com/guide/topics/sensors/sensors_motion https://developer.android.com/guide/topics/sensors/sensors_m.... You can run apps in the foreground basically infinitely, as long as the Android was not hacked to death by the vendor (and every new Android update might end that in the name of battery efficiency). One thing to keep in mind is that not every watch has every sensor. Not sure which ones you would need here, but gyroscope and distance should be needed. https://www.mobvoi.com/ge/pages/ticwatchse https://www.mobvoi.com/ge/pages/ticwatchse has both and would be a cheap starting point. Then this is "just" about creating a model that detects when the watch is in the target position. That might be impossible if I'm wrong about what the sensors return, or complicated if you need to create a complex model where in space the watch is at all time, or it might be rather easy - fully depends on what the sensor data give you and how far Android already interprets them.