A Review of Wrist-Worn Wearable: Sensors, Models, and Challenges

Table 4

Sensors used for activity recognition.

Sensor types	Activity studies
Accelerometer	[2, 3]
3-Axis accelerometer	[64–67]
Accelerometer and geomagnetic	[68]
Inertial measurement units: (i) Accelerometers; (ii) Gyroscopes; (iii) Magnetometers (sometimes)	[69]
Electric potential sensor	[70]
Multimodal sensors: (i) Activity (accelerometer and gyroscope); (ii) Ambient environment (temperature, atmospheric pressure, and humidity); (iii) Location context (Bluetooth message reception)	[63, 71]
Piezoresistive sensors and triaxial accelerometers	[72]
Ambient light	[16]
Heart rate (HR)	[67]