Electrodermal Activity (EDA) Stress Sensor

Sudomotor Drive

Sympathetic arousal 30%

Gland sensitivity 1.00×

Ambient temperature 24°C

Live Sensor Readout

Skin conductance

0.00 µS

Tonic baseline

0.00 µS

SCRs / min

Glands recruited

How it works

Skin conductance G(t) measured between two wrist electrodes is the sum of a slow tonic level (skin conductance level, SCL) and fast phasic bumps (skin conductance responses, SCRs) riding on top of it:

G(t) = G_tonic(t) + Σ SCR_i(t)

dG_tonic/dt = (G_target − G_tonic) / τ_tonic
G_target    = G_min + (G_max − G_min)·A(t) + k_therm·(T − 24°C)

SCR_i(t) = A_i·[ exp(−(t−t0,i)/τ_decay) − exp(−(t−t0,i)/τ_rise) ]

Each eccrine sweat gland fills with ionic sweat only when local sudomotor nerve firing exceeds its own recruitment threshold — glands with a low threshold switch on first as arousal A(t) rises, more join in as A(t) climbs further. The instanced dots on the wrist patch are individual glands; their glow intensity is that per-gland fill level, and the fraction lit up is exactly the "glands recruited" readout.

Sympathetic arousal — raises the tonic target G_target and the Poisson rate λ(A) = λ₀ + λ₁·A of spontaneous SCRs, matching real GSR under cognitive/emotional load.
Gland sensitivity — scales SCR amplitude A_i; models inter-person variability in sweat-gland density the wearable-biosensor literature cites as a source of measurement error.
Ambient temperature — drives thermoregulatory (not emotional) sweating, a separate additive term k_therm·(T−24°C) on the tonic baseline — the same confound that makes raw EDA hard to interpret outdoors.
Trigger stress event — injects one large-amplitude SCR (τ_rise ≈ 1–3 s, τ_decay ≈ 2–10 s), the classic startle-response waveform a wearable's onboard algorithm flags as a stress spike.

This is the same bi-exponential SCR + tonic-drift model used by consumer sudomotor sensors (Fitbit Sense's EDA scan, Empatica E4) and in psychophysiology research (Boucsein, Electrodermal Activity).

Active sweat gland Resting gland Electrode band

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