Dementia Signal Detection

A periodic worker (DementiaSignalWorker) runs every 60 s (configurable) and computes six signal kinds per tracked identity. Each signal is persisted via upsert with a deterministic UUID5 so the same detection window always maps to the same row.

Signal computation

All signals use robust z-scores (median + MAD) against per-person historical baselines fetched from the BehaviorBaselineRepository. A configurable hysteresis system prevents flicker:

• Onset debounce: a trigger condition must hold for min_consecutive runs (default: 2) before first emission.
• Cooldown: after emission, the same (identity, kind) is suppressed for cooldown_minutes (default: 60) unless severity escalates.
• Severity monotonic: within an active episode, severity only increases; the episode closes when the trigger condition clears.

Incremental window computation (enabled by default) merges new trajectory/dwell data with rolling state from previous runs, avoiding re-fetching the full 24-hour window on each cycle.

Signal kinds

Kind	Trigger	Baseline	Severity tiers
pacing	Repeated room transitions in a 30 min window, normalized for observation density. Minimum 8 transitions and 2 unique rooms. Purpose-driven ambulation (kitchen, living room, bathroom) typically produces 5-6 transitions; 8+ in 30 min identifies repetitive, purposeless movement.	30-day hourly activity transition rates	info (>0.15 rate), warning (>0.3 rate), emergency (rate-based)
sundowning_index	Evening (17:00-22:00 local) room transition rate vs 14-day evening baseline. Minimum 30 evening observation-minutes.	14-day evening-window activity	info (mod-z >= 2.5), warning (>= 3.0), emergency (>= 4.0)
bathroom_dwell_anomaly	Current open bathroom dwell vs 30-day closed-dwell duration baseline. Nighttime (22:00-06:00) uses a relaxed z-threshold (4.0 vs 3.5). Cold start (before 5+ baseline samples): absolute 45 min threshold, severity capped at warning. Requires accurate single-PH resolution at the bathroom door: the cross-camera dedup pass ensures a hallway camera and an adjacent camera seeing the same senior at the door produce one PersonHypothesis, so the dwell timer starts correctly. The integration proof for this scenario lives in tests/integration/test_world_tracker_e2e.py::test_hallway_bathroom_one_person, replaying tests/fixtures/frame_replays/hallway_bathroom_door.bin.	30-day dwell durations	info (z >= 3.5), warning (z >= 4.0), emergency (z >= 5.0)
nighttime_movement	Room transitions during 22:00-06:00 local time. Cold start: flat threshold of 3 transitions (one bathroom trip returns 2 transitions; 3+ indicates additional nocturnal movement).	14-day hourly activity	info, warning (z >= 3.0), emergency (z >= 4.0)
stillness_anomaly	Sustained near-zero motion energy in a non-resting posture (lying in non-bedroom, or prolonged sitting/standing). Default threshold: 60 min. Desk work, reading, and TV watching routinely exceed 30 min without clinical concern; 60 min aligns with clinical guidelines for meaningful seated immobility. Resting rooms are configurable (default: "bed", "bedroom").	30-day stillness episode durations	Posture-aware: lying starts at warning (escalates to emergency at 120 min); sitting/standing starts at info at threshold (upgrades to warning at 2× threshold)
absence	No detection for > 60 min (configurable). Cameras do not cover every room; 30 min gaps are normal (cooking, porch, bathroom). Hourly context from 14-day baseline: if the person is historically frequently absent at this hour, severity is demoted.	14-day hourly activity	info (>60 min), warning (>120 min), emergency (>180 min); demoted by expected_absence_prior

Signal structure

Each DementiaSignal carries:

Field	Description
signal_id	Deterministic UUID5 from (identity, kind, window_start, window_end)
identity_id	Tracked person
signal_kind	One of the 6 kinds above
severity	info, warning, or emergency
value	Raw metric value (rate, duration, transition count)
baseline	Historical median from the 30-day baseline
z_score	Modified z-score against the baseline
window_start / window_end	Detection window (UTC)
algorithm_version	Version stamp for signal evolution (currently 3)
context	Structured JSON payload with kind-specific details

Acknowledging a signal in the admin UI sets acknowledged_at, which the dementia_signal filter uses for cooldown.

Configuring signal thresholds

All signal thresholds are configurable via environment variables, with defaults set to clinically validated values. Override any threshold in the tracking orchestrator's config/settings.yaml or via environment variable:

# tracking-orchestrator/config/settings.yaml
signal:
  interval_s: "${SIGNAL_INTERVAL_S:-60}"
  stillness_threshold_minutes: "${SIGNAL_STILLNESS_THRESHOLD_MINUTES:-60}"
  stillness_emergency_minutes: "${SIGNAL_STILLNESS_EMERGENCY_MINUTES:-120}"
  stillness_motion_floor: "${SIGNAL_STILLNESS_MOTION_FLOOR:-0.02}"
  pacing_room_threshold: "${SIGNAL_PACING_ROOM_THRESHOLD:-8}"
  pacing_window_minutes: "${SIGNAL_PACING_WINDOW_MINUTES:-30}"
  nighttime_transition_threshold: "${SIGNAL_NIGHTTIME_TRANSITION_THRESHOLD:-3}"
  absence_threshold_minutes: "${SIGNAL_ABSENCE_THRESHOLD_MINUTES:-60}"
  bathroom_absolute_threshold_seconds: "${SIGNAL_BATHROOM_COLD_START_S:-2700}"

Environment variable	Default	Description
SIGNAL_INTERVAL_S	60	How often the signal worker runs (seconds)
SIGNAL_STILLNESS_THRESHOLD_MINUTES	60	Minimum stillness duration before triggering stillness_anomaly at info severity
SIGNAL_STILLNESS_EMERGENCY_MINUTES	120	Stillness duration that escalates lying posture to emergency severity
SIGNAL_STILLNESS_MOTION_FLOOR	0.02	Motion energy below this value is treated as stillness. Normal physiological ambient motion (breathing, micro-adjustments) is approximately 0.01-0.02.
SIGNAL_PACING_ROOM_THRESHOLD	8	Minimum room transitions in the pacing window to trigger pacing
SIGNAL_PACING_WINDOW_MINUTES	30	Rolling window for pacing transition counting (minutes)
SIGNAL_NIGHTTIME_TRANSITION_THRESHOLD	3	Cold-start flat threshold for nighttime_movement (transitions per night)
SIGNAL_ABSENCE_THRESHOLD_MINUTES	60	Minimum undetected duration before triggering absence at info severity
SIGNAL_BATHROOM_COLD_START_S	2700	Cold-start absolute threshold for bathroom_dwell_anomaly (seconds; 2700 s = 45 min)