The rise of wearables. Along with the uptake of sensor-rich smartphones, we are also witnessing the diffusion of sensorequipped
wearable devices. After a first generation of standalone wearable devices, we now have a second generation of
wearable computers designed for smartphone interaction. The research community, however, focused on wearable sensing
several years before mobile phones became sensor-rich. The current uptake of wearable devices was already predicted at
the turn of the century [102], and there were a few initial efforts in indoor navigation [103] and context recognition based on
wearable sensors [104]. For the most part, the seminal contributions in the wearable sensing space date back to the middle
of the past decade.