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Ride Recall - NUI-driven in-cabin occupant monitoring for the connected car

Oct 2024 - Feb 2025 · THI × AVL

In collaboration with AVL (Austria), Ride Recall detects forgotten items and rear-seat occupants after a vehicle is parked - combining pressure-sensor fusion, camera-based AI detection, and a tiered mobile notification UX. Published at ACM AutoUI 2025.

  • UX Research & Strategy
  • Interaction Design
  • Mobile App UI
  • Hardware Prototype
  • ACM Conference Paper
NUI · Automotive · ACM AutoUI 2025

The car
remembers.

An in-cabin monitor that alerts drivers to forgotten passengers and belongings - before they walk away.

Prototype Demo
Occupant Monitoring· Natural User Interface· Sensor Fusion· ACM AutoUI 2025· Automotive UX· Edge AI Detection· Tiered Notifications· User Research· Occupant Monitoring· Natural User Interface· Sensor Fusion· ACM AutoUI 2025· Automotive UX· Edge AI Detection· Tiered Notifications· User Research·

Every year, children and pets die in hot cars. Forgotten bags and medications cause daily stress. Ride Recall turns a parked vehicle into an intelligent guardian - sensing what's left behind, and who.

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Project duration
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User interviews
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Prototype iterations
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Published ACM paper
ACM AutoUI 2025
Ride Recall: A UX Case Study in Automotive Occupant Monitoring
ACM International Conference on Automotive User Interfaces and Interactive Vehicular Applications

Existing driver monitoring systems focus entirely on safety during the drive. The moment the engine stops, cabin awareness disappears - creating a window where the most dangerous forgetting happens.

Monitoring stops
the moment the
car does.

Rushed departures, rental handovers, and distracted drop-offs create a "forgetfulness gap" - a window between engine-off and building entry where no system watches the cabin. Ride Recall closes that gap.

A dual-layer sensor system: pressure-sensitive seat mats detect mass, a wide-angle IR camera confirms what's there. All classification runs on the edge - no cloud, no latency, no data leaving the car.

Detect
Weight Sensing
Pressure mats under each seat detect any remaining mass the moment the driver exits the vehicle.
01
Confirm
AI Vision
A headrest-mounted IR camera classifies objects and living occupants in real time, distinguishing a sleeping child from a laptop bag.
02
Classify
Severity Model
Detections are scored by urgency: living occupants trigger Critical; valuables trigger Alert; everyday items get a silent Reminder.
03
Alert
Push Notification
A tiered notification reaches the driver's phone in under 3 seconds, with the right urgency, before they are out of range.
04

A research-grade prototype assembled from off-the-shelf hardware: pressure sensor mats, Raspberry Pi, and a wide-angle IR camera. Three iterations before the study - each refining detection accuracy and alert latency.

Pressure Mats

One per seat, detecting weight distribution to distinguish a child's mass from a laptop bag - even on similar pressure readings.

IR Camera Module

Wide-angle, headrest-mounted. Full rear-cabin coverage in daylight and low-light. Object classification runs entirely onboard.

Edge Processing

All detection logic on a Raspberry Pi. Sub-3-second park-to-notification. No cloud dependency, no privacy risk.

Every component chosen for reliability, low cost, and edge-first processing. No cloud dependency means no latency, no privacy exposure, and no single point of failure.

Detection Layer
Pressure + Vision
Dual-sensor fusion: FSR pressure mats confirm mass presence, a wide-angle IR camera validates and classifies what is there. Neither layer alone is sufficient - both are required before an alert fires.
Processing
Raspberry Pi 4B
Onboard CV model runs in under 800ms per frame. No internet required. The entire detection-to-push pipeline completes in under 3 seconds.
Sensors
FSR Seat Mats
Force-sensing resistor mats placed under each seat cushion. Detect weight distribution and discriminate between a child and a bag on similar pressure readings.
Optics
Wide-angle IR Camera
Headrest-mounted, 160-degree field. Full rear-cabin coverage in daylight and near-zero light. Object and pose classification via MobileNet-based model.
UX Stack
Figma + React Native
Complete design system in Figma. Prototype built in React Native for iOS - real notification delivery via APNs, real dismissal flows, real data logging.

Twelve semi-structured interviews with daily drivers. Two mental models emerged: routine neglect and situational neglect. Both groups strongly preferred a phone notification over in-car audio - and tiered severity over a single undifferentiated alert.

Finding 01

"I only realise I've left something once I'm three floors up." Realisation, not forgetting, is the highest-stress moment - 8 of 12 participants confirmed this pattern.

Finding 02

Users tolerated false positives for objects, but not for living passengers. A smart severity model - not a blanket alarm - was essential for long-term trust.

Finding 03

Drivers preferred phone notification over in-car audio. Privacy in shared spaces mattered - a discreet buzz beats a public announcement.

Three severity tiers. Each determines vibration pattern, sound, visual treatment, and escalation behaviour. The urgency of the message always matches the nature of what was found.

Critical - Living Occupant or Pet
Full-screen takeover, persistent haptic. Triggers an emergency contact call if unacknowledged after 60 seconds. Cannot be silenced, only dismissed after confirmation.
Alert - High-Value Item
Sound + haptic for medication, electronics, or groceries. Requires explicit acknowledgment. Event is logged with timestamp and location.
Reminder - Low-Priority Item
Silent banner for shopping bags, umbrellas, or low-risk objects. Auto-dismissed if the driver returns within 10 minutes.

Designed for one-handed, glance-first interaction. Dark backgrounds match the automotive context. Alert hierarchy uses colour and scale - legible in bright sunlight, unambiguous in a rush.

Home screen
Item detected

Home & Detection

You've left your car 3 min ago.

The home screen greets the driver with their rented car, a map to it, and any active detections - everything needed to act, in one glance.

Detail & Resolution

Retrieve it, or let it go.

The detail screen shows a camera snapshot of the item, its seat location, and timestamp. Two choices: retrieve it now, or mark it as intentionally left. Every decision is logged.

Item details
Confirmed safe

A within-subjects study with real participants: place an item in a parked car, exit, receive a notification, evaluate clarity and urgency. Conditions varied detection type, severity tier, and dismissal interaction - results published at ACM AutoUI 2025.

A five-person team across UX, hardware, and machine learning. End-to-end ownership of the user experience: from initial research through notification design, prototype testing, and co-authorship of the published paper.

My Contribution
UX Research + Design
User interviews, journey mapping, lo-fi wireframes, notification system design, mobile app UI (all screens), design system in Figma. Sole author of the UX methodology chapter.
Team
Hardware + CV Engineering
Sensor mat fabrication, Raspberry Pi integration, IR camera mount, MobileNet-based object classifier, real-time FSR signal processing pipeline.
Output
ACM AutoUI 2025 Paper
Co-authored and published at the ACM International Conference on Automotive User Interfaces. Full methodology, prototype specs, user study results, and future work.

Zero misses.
Zero noise.

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Living Occupant Detection

Every simulated child and pet triggered a Critical alert. Zero misses across all lighting conditions tested.

0s

Park-to-Alert Time

Under 3 seconds from engine-off to notification delivery.

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Alarm Fatigue Reduction

Tiered model reduced dismissal-without-reading by 68% vs. a single-tier alert.

"A car that knows when you've left something or someone behind."

Ride Recall · ACM AutoUI 2025