Table 3.

Features of wearable devices used for blood glucose forecasting or prediction.

Authors	Wearable technology type	Wearable device type	Placement of wearable device	Device technology or brand	Sensing approach		Devices, n		Sensing type			Gateway		Host device	Mode of data transfer
Hina et al [22]	Prototype	Wearable sensor	Finger	N/Aa	Participatory		1		NIRb, PPGc		N/A			N/A	N/A
Alfian et al [23]	Commercial	Smart wristband	Wrist	Mi Band 2: Mi Band 2, Mi Smart Scale, Caresens, and Omro	Participatory		4		BLEd sensors		Smartphone			Cloud	Bluetooth
Alarcon-Paredes et al [24]	Prototype	Wearable sensor	Hand	N/A	Participatory		1		PPG sensor and GSRe sensor		N/A			N/A	N/A
Islam et al [8]	Prototype	Wearable sensor	Finger	Raspberry Pi Zero	Participatory		1		Raspberry Pi camera		N/A			Smart devices	Internet
Kularathne et al [25]	Prototype	Wearable sensor	Foot	Raspberry Pi Zero	Opportunistic		1		Tilt switch sensor, calibrated load cell sensor, DHT22f		N/A			Smart devices	Internet
Joshi et al [26]	Prototype	Wearable sensor	Finger	N/A	Opportunistic		1		NIR		Smartphone			Cloud	Internet
Zhou et al [27]	Commercial	Smart watch	Wrist	Glutrac	Opportunistic		1		NIR and ECGg		Smartphone			Cloud	Bluetooth
Mahmud et al [28]	Prototype	Smart watch and wearable sensor	Wrist	Arduino Nano, Raspberry Pi	Opportunistic		2		PPG, temperature, GSR sensors		N/A			Raspberry Pi	Wired
Bent et al [29]	Commercial	Smart wristband	Wrist	Empatica E4	Opportunistic		1		PPG, ACCh, EDAi, or GSR sensor, infrared thermopile		Smartphone or PC			Cloud	Bluetooth
Lee et al [9]	Prototype	Smart watch	Wrist	Custom	Opportunistic	1		PPG and NIR		Smartphone			Cloud			Bluetooth
Shrestha et al [30]	Prototype	Smart wristband	Wrist	N/A	Participatory	1		Metal oxide semiconductor–based chemical sensors		Smartphone			Cloud			Bluetooth
Li et al [31]	Prototype	Wearable sensor	Wrist	Custom	Opportunistic	1		NIR		N/A			None			N/A

^aN/A: not applicable.

^bNIR: near-infrared.

^cPPG: photoplethysmography.

^dBLE: Bluetooth low energy.

^eGSR: galvanic skin response.

^fDHT22: digital-output relative humidity and temperature sensor.

^gECG: electrocardiogram.

^hACC: accelerometer.

ⁱEDA: electrodermal activity.