Table 2.

Sensor characteristics.

Study	Type of sensor	Testing conditions	Role of sensor	Sensor measures	Sensor-linked intervention	Sensor usability and acceptability
Chung et al [26], 2021	Lief Smart Patch; worn on torso under clothing	Continuous wear in everyday life	Reduce anxiety	HRa, HRVb, and accelerometer data through continuous monitoring	HRVBc wearable device and remote stress management coach	86% of participants wore the patch and completed ≥1- to 3-min HRVB exercise on at least 40 of 56 days; only 43% completed 3 or more 3-min HRVB exercises on at least 40 of 56 days
Crivelli et al [27], 2018	Lowdown Focus brain-sensing eyeglasses	Wore glasses when participating in meditation practice	Stress management	EEGd activity	Vipasyana meditation and technology-mediated mental training for stress management (which involved real-time acoustic feedback via an app based on changes in physiological signature of the participants’ mindset)	Not reported
Jaramillo-Quintanar et al [28], 2020	i-CARE; sensor on child’s finger	Lab administered	Regulate symptoms of anxiety	HR, blood oxygenation, and infrared measurements of facial temperature	i-CARE, which measures HR and blood oxygenation, and provides visual and auditory biofeedback	Not reported
Kizakevich et al [29], 2019	BART; chest belt sensor	Continuous wear in everyday life	Manage anxiety	HRV	4 different resilience training techniques each with or without HRV biofeedback; continuous acquisition of HRV data enables analysis of physiological response to stress and breathing training	Participants in the 6-week training regimen completed; 600 sessions during the first week; however, over the next several weeks, training compliance fell by almost one-third and to about one-half after 1 month
Millings et al [30], 2015	Prototype wearable sensor kit	Continuous wear in everyday life	Stress management	HRV, HR, and physical activity	Stress management program and a prototype wearable sensor kit comprising of an ECGe and EEG sensor	Qualitative results found that many participants experienced technical issues that caused frustration
Nguyen et al [31], 2021	Wearable Shimmer2 unit	Lab administered	Manage anxiety	HR, anxiety-level feedback on tablet (green: calm; yellow: rising anxiety; red: anxious)	Use of anxiety meter and breathing techniques	Not reported
Ponzo et al [32], 2020	Biobeam; wrist worn; continuous wear	Continuous wear in everyday life	Manage stress and anxiety	Sleep duration and quality, HR, step count	Biobase program, mobile app comprising psychoeducational content, mood tracking via EMAf and in-the-moment exercises (eg, relaxation); real-time sensor data presented to user via app dashboard	Not reported
Shruthi et al [33], 2021	Prototype wrist band	Continuous wear in everyday life	Manage anxiety	Oxygen levels, water intake, sleep, HR	Wrist band that provided acupressure to the H7 point on the wrist crease when completing a stressful task vs group wearing Fitbit-like band	Not reported
Serino et al [34], 2014	App called Positive Technology	Worn when using the app (not well defined)	Manage stress	HR	App that teaches guided relaxation, 3D biofeedback training, and stress self-tracking	Not reported
Smith et al [35], 2020	Device called Spire Stone: a clothing-attached device	Continuous wear in everyday life	Manage stress and anxiety	Respiratory effort and physical activity	App that delivers mindfulness-based breathing from MBSRg and Spire Stone to measure subjective emotional state changes; both provide biofeedback about physiological state; the app provided push notifications	Participants wore the device 52% of the days during the intervention period; 75% completed at least one educational guided breathing session and only 19% completed all 5 sessions
Winslow et al [36], 2016	E3 band, wrist worn	Continuous wear in everyday life	Manage stress	PPGh, EDAi, body temperature, accelerometer, HR	In-person CBTj + sensor and mobile app; alerted the user through the app when stress was detected and presented with prompts or reminders to engage with stress mitigation techniques	Individuals in the experimental group completed a significantly greater number of therapy sessions compared to the control group; 1 participant in the experimental group did not use the app but completed CBT

^aHR: heart rate.

^bHRV: heart rate variability.

^cHRVB: heart rate variability biofeedback.

^dEEG: electroencephalogram.

^eECG: electrocardiogram.

^fEMA: ecological momentary assessment.

^gMBSR: mindfulness-based stress reduction.

^hPPG: photoplethysmography.

ⁱEDA: electrodermal activity.

^jCBT: cognitive behavioral therapy.