Calmables: Demonstrating Closed-Loop Infrared Earables for Thermal Biofeedback and Relaxation Support

1 Introduction

• Brief recovery opportunities are constrained by ongoing work and study obligations, while established relaxation practices can require dedicated time, attention, or a supportive environment.This motivates subtle biosignal-adaptive cues that do not rely on screens or audio.Source: §1 · p. 2
• Prior work links thermal stimulation and comfort to stress-related subjective states, but most work focuses on other body regions or thermal comfort rather than acute stress recovery.Heated headphones and in-ear infrared systems have explored thermal comfort and perception.Source: §1 · p. 2
• Calmables applies closed-loop infrared ear warming to an acute stress-recovery scenario, letting attendees compare manual and heart-rate-responsive cues against a resting baseline.The demo explores whether active stimulation changes subjective recovery and can be delivered in a perceivable, comfortable, and interpretable way.Source: §1 · p. 2

Subtle Wearable Cues for Recovery

• Wearable biofeedback has used vibrotactile, rhythmic, and interoceptive cues for down-regulation, but lightweight closed-loop systems translating physiological signals into subtle interventions remain comparatively underexplored.Calmables treats heart rate as an inspectable control signal, not a specific stress detector.Source: §2 · p. 2

Thermal Cues and Actuation

• Thermal cues offer a private, low-attention wearable modality that can be experienced without screens or sound, and Calmables makes this feedback directly perceivable in a short walk-up interaction.Prior work indicates stimulation location can shape comfort, perceptibility, and perceived restfulness.Source: §2 · p. 2
• Thermal stimulation and comfort have been linked to autonomic and subjective regulation, but these findings do not directly establish ear-localized warming as an acute stress-recovery intervention.Prior infrared and photobiomodulation work primarily reports subjective relaxation, sleep, or well-being outcomes.Source: §2 · p. 2
• Ear-worn systems offer a familiar wearable platform, and prior heated headphones and in-ear infrared systems explored thermal comfort and perception; Calmables extends this context to acute stress recovery.The demo lets attendees experience active warming, compare manual and heart-rate-responsive behavior, and inspect triggering.Source: §2 · p. 2

3 Calmables: Closed-Loop Infrared Earables

• Calmables reuses Heatables’ in-ear IR/NIR-LED actuator and adds BLE communication, smart-ring processing, baseline-relative control, visualization, and guided interaction.The ring streams PPG/IMU data to the phone, while the earable reports temperature and shuts down on connection loss or faults; stimulation is disabled at 50 °C.Source: §3 · p. 2, §3.1 · p. 2, Figure 2 · p. 3

3.1 Data and Control Flow

• A session baseline comes from a 30-second seated calibration or manual entry, with the trigger set to mean calibration HR plus three standard deviations; stimulation turns on after three above-threshold samples and off after three below the hysteresis threshold.Manual mode permits direct PWM control when HR remains near baseline.Source: §3.1 · p. 2

3.2 Heart Rate Assessment

• Green PPG is filtered and IMU-compensated; MSPTDfast-derived interbeat intervals feed a Kalman HR estimate whose measurement noise adapts to signal quality, suppressing bad or unavailable updates.The four signal-quality states are good, fair, bad, and unavailable.Source: §3.2 · pp. 2–3

3.3 Preliminary UX Comparison

• The initial evaluation followed MAST stress induction with 18 participants wearing Calmables or a visually similar placebo during a 15-minute recovery period, followed by 1–7 Likert ratings and corrected one-sided bootstrapped tests.Comparisons used 10,000 bootstrap samples and Bonferroni correction at 0.0071.Source: §3.3 · p. 3
• Active ratings exceeded placebo for perceived relaxation (MC = 5.50, MP = 2.80; p = 0.0004) and perceived recovery support (MC = 5.62, MP = 2.90; p = 0.0013).Figure 3 presents ratings after the recovery scenario for the active prototype and visually similar placebo.Source: §3.3 · p. 3, Figure 3 · p. 3

4 Demonstration

• Dashboard mode displays live HR, baseline, trigger threshold, and stimulation level, allowing manual PWM intensity exploration or HR-responsive control.Attendees can compare manual and automatic control in an open-ended interaction.Source: §4 · p. 4
• The guided demo previews warmth and selects a comfortable intensity, measures a 30-second baseline, then uses paced rapid breathing to raise HR until the personalized trigger activates warming.An optional demo trigger starts the same actuation path if the threshold is not reached within 20 seconds, without altering or simulating HR.Source: §4 · p. 4
• After activation, participants breathe normally while warming continues for at least 25 seconds and ends below the hysteresis threshold; the flow records warmth and relaxation ratings and summarizes the run.A manual end becomes available after 30 seconds, and repeated phone vibration marks completion until confirmed.Source: §4 · p. 4
• Across both modes, HR is an inspectable control signal rather than a reliable stress classifier, and stimulation uses the same BLE path with device-side safety enforcement.The modes combine open exploration with a repeatable end-to-end experience.Source: §4 · p. 4

• A preliminary placebo-controlled UX comparison suggests active infrared stimulation changes the subjective recovery experience while remaining comfortable.Source: §5 · p. 4
• The demo combines smart-ring heart-rate sensing, smartphone processing and visualization, and safe infrared warming through BLE-controlled Heatables.Source: §5 · p. 4
• Attendees can experience ear-localized warming, compare manual and heart-rate-responsive modes, and inspect how baseline-relative heart rate triggers stimulation.Source: §5 · p. 4
• The authors call for larger, more diverse placebo- and treatment-controlled studies combining subjective recovery items with physiological markers.Suggested markers include HRV, respiration, salivary cortisol, and alpha-amylase.Source: §5 · p. 4