The advent of mobile phone sensing. For the most part, the mobile phone was initially viewed as a high-end gateway-like
device that could interface a sensor network with the outside world and take care of advanced processing tasks that could not
be handled by low-end motes; representative efforts in this direction include the Phone System Interface board [73] (a sensor
network gateway that plugs into the MMC/SD-card socket of a phone), the Healthgear system [74], whose wearable low-end
sensor nodes use Bluetooth to communicate to a cell phone that processes their data, and Dartmouth’s Bikenet [75], where
several bicycle- and human-mounted low-end motes report to a mobile phone through a 802.15.4-to-Bluetooth interface.
Compared to low-end motes, the mobile phone was viewed as a higher-end device with a lot more computing power and
much more relaxed energy constraints. As the transition from feature phones to smartphones started happening, it became
clear that the mobile phone itself had extensive sensing capabilities and could therefore double as a mobile sensing device.