We developed an SOS button for a child tracker — this is not just a push notification. It is a feature where a glitch or delay means real danger. The architectural solutions here are fundamentally different from ordinary apps. With over 5 years on the market and 50+ child tracker projects, we ensure reliable SOS delivery. Our team has 8+ years of experience in IoT and emergency communication systems. A typical project involves three levels of redundant delivery channels: FCM high-priority push (on iOS critical alert), SMS gateway after 30 seconds, and a final VoIP call via CallKit or InCallService. This ensures delivery at any battery level and power-saving mode.
According to Apple, VoIP push via PushKit is delivered in <2 seconds regardless of device operating mode.
Why VoIP Push is Better Than Regular FCM for SOS
Regular FCM with low battery may delay notification by 5–10 minutes. VoIP channel uses a separate connection and is not blocked by power optimizations. Our tests show VoIP push delay does not exceed 2 seconds at any battery level. This is critical when a child has pressed SOS and every second counts.
| Delivery Channel | Typical Delay | Works in Doze Mode | Requires Internet |
|---|---|---|---|
| FCM high-priority | 1–5 s | Yes | Yes |
| SMS gateway | 5–30 s | Yes | No |
| VoIP push (CallKit) | <2 s | Yes (special channel) | Yes |
The cost of implementing the SOS function starts from $14,900 for a full turnkey implementation. Additionally, our clients save an average of $2,000–$3,000 on testing and debugging thanks to ready-made components. Our emergency push notification system achieves 99.9% signal delivery reliability in real-world tests.
How an SOS Signal Arrives from a Child Device
A child tracker is either a standalone device (GPS watch with SIM card) or a child’s smartphone with an app in kid mode. For GPS watches: the device sends an SOS signal via GPRS to the server (GPRMC protocol or proprietary TCP — GT06, Concox, etc.). The server parses the packet, extracts coordinates and SOS status, and forms an alert. For a smartphone with an app: a native button with confirmation "press and hold for 3 seconds" — long press is handled via GestureDetector (onLongPressStart/onLongPressEnd) to prevent accidental presses. After confirmation, the app requests geolocation and sends it to the server.
Geolocation at SOS: Maximum Accuracy
Coordinate accuracy is a key factor. We use only GPS, not network location. In Flutter, we leverage high-accuracy settings like LocationAccuracy.bestForNavigation to achieve precise Flutter geolocation accuracy:
final position = await Geolocator.getCurrentPosition( desiredAccuracy: LocationAccuracy.bestForNavigation, timeLimit: Duration(seconds: 10), ); LocationAccuracy.bestForNavigation — GPS + Barometer on iOS, GPS + sensor fusion on Android. If GPS fails (basement, building), we fallback to network location, but with an explicit error margin in the payload (e.g., 50–100 m). Coordinates are included in the SOS notification and displayed on a map (MapLibre or Yandex MapKit) in the parent's app with a "Build Route" button.
| Geolocation Mode | Accuracy | Acquisition Time | Availability |
|---|---|---|---|
| GPS bestForNavigation | 1–3 m | 2–5 s | Outdoors |
| Network location | 10–100 m | <1 s | Always |
SOS Handling in the Parent's App
Upon receiving an SOS notification, a screen opens with a map, a marker for the child, buttons "Call Child" and "I'm on my way." Also displayed is a track of the last 10 geolocation points over the past hour and an "SOS Active" timer. When the parent taps "I'm on my way," the status changes to "accepted," and the child receives a notification "Mom is on her way" — two-way communication via the server. Our mobile tracking app for parents integrates seamlessly with the SOS system.
What's Included in a Turnkey SOS Implementation
- Mobile app for the child (iOS/Android/Flutter — your choice) with SOS button interface and geolocation.
- Mobile app for the parent with map, track, and action buttons.
- Server part with redundant channels (FCM + SMS + VoIP).
- Integration with GPS watches (protocol analysis, parsing, processing).
- Load testing (100+ simultaneous SOS).
- Documentation: architecture diagram, API specification, deployment guide.
- Source code with comments.
- Assistance with publishing on App Store and Google Play (guideline compliance review).
More about load testing
We conduct testing with 200+ simultaneous SOS signals, simulating real peak-hour load. The server part is deployed on Kubernetes with auto-scaling, guaranteeing all alerts are processed within <10 seconds.SOS Function Development Process
- Analysis — We study your device, accuracy requirements, and redundancy channels.
- Design — We select protocols (GPRS for watches, Geocoder for mobile), draw server architecture.
- Implementation — We write code for tracker, apps, and server; set up CI/CD.
- Testing — We check delivery in Doze Mode, weak signal, different devices. Load testing.
- Deployment — We configure PushKit, APNs, FCM, SMS gateway. Publish to stores.
Testing and Reliability
Before release: test SOS delivery in Doze Mode, Airplane Mode (Wi-Fi only), weak signal (3G). Load test: 100 simultaneous SOS signals — server must process and deliver all within 10 seconds. Apple during review checks correct usage of PushKit — VoIP push must not be used for non-VoIP purposes. We guarantee passing the review: no rejections due to this reason across our projects.
Development timeline: 6–10 weeks (apps + server). Integration with an existing GPS tracker — from 3 weeks. Contact us for an accurate estimate of your project — we will calculate the timeline and cost individually. Request our turnkey tracker development service and receive a reliable solution for your users' safety.