SentinelKids
Parent-Child Digital Safety & Device Management Platform
At a Glance Proof
Delivered a resilient parent-child monitoring infrastructure processing high-frequency device telemetry with sub-200ms alert propagation, real-time web filtering, instant app blocking, and multi-device synchronization across zero-rollback releases.
Architected the backend telemetry ingestion pipelines using Node.js and Express.js, designed PostgreSQL relational schemas for family hierarchies and device state, implemented Socket.io connections for real-time streaming, integrated PubNub for distributed state caching, and configured Firebase Cloud Messaging for instant push notifications to the React Native and Flutter clients.
Node.js & Express.js backend services · PostgreSQL relational database · Socket.io real-time connection · PubNub real-time state sync & cache · Firebase push notifications · React Native (Parent App) · Flutter (Child App)
Project Overview
Modern parents struggle to protect children from online harms, excessive screen time, and physical safety risks without resorting to invasive surveillance. SentinelKids required an ultra-reliable, battery-efficient dual-app platform capable of continuous telemetry, low-latency parent notifications, robust web filtering, and granular app management.
Target Users: Parents managing child well-being, children using connected mobile devices, and operations engineers monitoring streaming health.
- ▹Alert latency must stay strictly under 200ms for safety-critical geofence crossings and emergency SOS events.
- ▹Child background service must maintain minimal battery drain (<3% daily impact) despite continuous GPS and telemetry sync.
- ▹High-frequency telemetry spikes across thousands of concurrent child devices cannot saturate or degrade database writes.
- ▹System must enforce strict COPPA/GDPR-K child privacy standards with end-to-end encrypted device-to-parent tunnels.
Platform Capabilities & Feature Architecture
Comprehensive architectural breakdown covering user-facing controls, background services, and automated workflows.
Parent & Child Ecosystem & Secure Pairing
Dedicated dual-app architecture tailored strictly for parents and children
- ▹SentinelKids Parent App (React Native): Centralized command dashboard for parents to configure safety rules, monitor live locations, review usage reports, and trigger instant device locks.
- ▹SentinelKids Child App (Flutter): Lightweight, battery-optimized background service installed on the child device enforcing system rules, intercepting URLs, and streaming telemetry.
- ▹Cryptographic QR Pairing: 60-second out-of-band device onboarding establishing mutual authenticated trust between parent account and child hardware.
- ▹Tamper & Uninstall Protection: Alerts parents immediately if accessibility permissions, device administration, or the child background daemon are tampered with.
Real-Time Child Data & Telemetry Sync
Continuous tracking of child safety, device vitals, and digital health
- ▹High-Precision GPS Tracking: Live map updates with breadcrumb trail history, movement velocity, and accuracy confidence intervals.
- ▹Battery & Network Monitoring: Proactive alerts when a child's device drops below critical battery thresholds (e.g. 15%) or loses network connectivity.
- ▹Active Screen Time Telemetry: Real-time calculation of daily screen usage, active foreground applications, and device unlock frequencies.
- ▹Socket.io & PubNub Synchronization: Bidirectional real-time telemetry streaming maintaining active connection states and sub-second updates across parent and child devices.
- ▹Zero-Data-Loss Offline Buffering: Local SQLite caching on the Flutter child device ensuring telemetry beacons upload smoothly via Socket.io once connectivity is restored.
Web Filtering & Safe Surfing Engine
Dynamic content filtering blocking inappropriate, adult, and malicious websites
- ▹Multi-Category Content Blocker: Automated DNS and URL inspection blocking adult content, gambling, violence, weapons, and phishing sites in real time.
- ▹Enforced Safe Search: Automatically forces SafeSearch on Google, Bing, and restricted mode on YouTube across all mobile browsers.
- ▹Custom Blacklist & Whitelist: Allows parents to add specific domain exemptions or block custom websites instantly from the Parent App.
- ▹Real-Time Web Browsing Logs: Detailed visibility into domains visited, search queries, and timestamped blocked access attempts.
App Blocker & Application Inventory Management
Granular app-level management and instant application locking
- ▹Live Application Inventory: Automatically catalogs every new app installed on the child device and sends an alert to the parent dashboard.
- ▹One-Tap Instant App Lock: Instantly shut down access to specific distracting apps (social media, games) without affecting school or phone tools.
- ▹Per-App Time Limits: Set strict daily quotas on specific entertainment apps (e.g., 30 minutes max on video streaming per day).
- ▹New App Installation Approval: Optional gating preventing children from launching newly downloaded apps until parent approval is granted.
Routines & Screen Time Scheduling
Automated daily schedules for bedtime, study, and family routines
- ▹Scheduled Bedtime Lockdown: Enforces complete device lockdown during sleep hours, leaving only emergency phone calling accessible.
- ▹Education & Study Mode: Blocks social media and games during homework hours while keeping educational apps and calculators active.
- ▹Dinner & Downtime Routines: One-tap 'Pause All Devices' routine for family dinners or study sessions.
- ▹Daily Time Allowances: Global screen time limits that automatically disable entertainment once the daily threshold is met.
Geofencing Safe Zones & Instant Alerts
Geographical boundaries with sub-200ms Firebase push alert dispatch
- ▹Custom Safe Zones: Circular and polygonal geofences around Home, School, Grandparents' House, and Sports Centers.
- ▹Entry & Departure Triggering: Millisecond boundary evaluation generating instant alerts the moment a child arrives or departs.
- ▹SOS Emergency Beacon: Instant one-tap child distress alert that broadcasts exact coordinates to parents with maximum alarm priority.
- ▹Sub-200ms Firebase Push Dispatch: Real-time event pipeline evaluating geofence triggers and routing alerts through Firebase Cloud Messaging (FCM) to parent devices in under 200 milliseconds.
Product Flow & System Context
Child mobile daemons (built in Flutter) stream real-time telemetry and rule validation queries over Socket.io into high-performance Node.js and Express ingestion gateways. Live state is coordinated through PubNub real-time streams and cached state buffers, persistent records commit to PostgreSQL, and safety triggers dispatch push notifications to the React Native Parent App via Firebase Cloud Messaging.
Tech Stack and Runtime Architecture
Parent Mobile App
Central parent command center for live location maps, routine schedules, app locks, and Firebase push alerts.
Child Mobile App & Background Daemon
Child client running background telemetry, URL interception, screen time calculation, and local app blocking.
API & Ingress Gateway
Terminates client connections, validates DTO payloads, and orchestrates device authentication.
Real-Time Telemetry & Sync Layer
Maintains bidirectional real-time sockets with child and parent clients, synchronizing state changes and caching active child vitals.
Persistent Relational Database
Stores parent accounts, family hierarchies, device pairings, schedule policies, and historical telemetry logs with relational integrity.
Push Notification Worker
Subscribes to high-priority alert triggers and dispatches instant parent push notifications.
Critical Execution Flow
Child Safe-Zone Departure & Instant Parent Alert Flow
How a child leaving a designated School safe zone triggers spatial evaluation, event queueing, and sub-200ms parent push notification.
Child Daemon Telemetry Capture
Flutter child device registers GPS movement and emits an encrypted location telemetry beacon via Socket.io to the Node.js/Express gateway.
Spatial Ray-Casting & PubNub Publish
Edge worker verifies coordinates against safe zone polygon boundaries, detects exit boundary violation, and immediately broadcasts a boundary event through PubNub.
Database Record & Alert Payload Formatting
System commits the incident to PostgreSQL and constructs a localized, high-priority notification payload for the parent account.
Parent Notification & Live Map Lock
Parent receives high-priority Firebase push alert in <180ms; opening the notification launches the React Native Parent App focused on the child's live moving location.
Architectural Decisions & Trade-Offs
| Decision | Alternatives Considered | Why Chosen | Cost / Risk Accepted | Quality Attribute |
|---|---|---|---|---|
| Socket.io and PubNub data stream pipeline for real-time telemetry and state sync | Periodic HTTP client polling, custom raw TCP socket servers | Socket.io provides lightweight bidirectional communication with automatic fallback, while PubNub delivers managed pub/sub state caching across mobile clients with minimal battery consumption. | Required maintaining socket lifecycle states and reconnections when mobile devices switch between Wi-Fi and cellular. | Performance, Low Latency & Battery Efficiency |
| PostgreSQL relational schemas with foreign key constraints for family hierarchies | Unstructured document stores without schema enforcement | Safety-critical parent-child pairing, routine schedules, and geofence rules require strict relational consistency, ACID guarantees, and referential integrity. | Required structured database migration scripts and index optimization for high-frequency location history tables. | Data Integrity & Reliability |
| Dedicated Flutter for Child App and React Native for Parent App | Single shared hybrid framework for both applications | Flutter compiles directly to native machine code with fine-grained access to OS accessibility APIs and battery-efficient background daemons for the child device; React Native provides rapid component modularity and seamless native bridge access for the parent dashboard. | Required coordinating two distinct mobile codebases and client SDK contracts. | Modularity, Native Device Control & Performance |
What We Delivered & Future Roadmap
- ✓End-to-end dual app pairing flow linking SentinelKids Parent App and SentinelKids Child App via secure QR handshake.
- ✓Sub-200ms latency across core monitoring, safe zone geofence exits, and emergency alert dispatch paths.
- ✓Dynamic web filtering and safe search engine blocking unauthorized URLs and harmful web categories.
- ✓Application blocker and routine scheduling system enforcing bedtime and homework screen time limits.
- ✓Zero rollback release cadence achieved through reproducible Docker builds and staging verification.
- →Automated dead-letter queue (DLQ) re-drive tooling with operator self-service dashboard.
- →Dynamic auto-scaling of worker consumer pods based on active consumer lag thresholds.
- →On-device lightweight machine learning for intelligent anomaly and driving-speed detection.
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