How can I implement offline SOS functionality in a PWA with SMS fallback?

[ankan123basu]

I'm researching offline-first safety solutions and came across SheShield — amazing concept!

I was wondering: how would you implement an emergency SOS feature in a PWA that works even without internet?

I’m specifically curious about:

• Allowing the user to trigger SOS when offline
• Using the device’s SMS as a fallback
• Storing the alert locally (like IndexedDB)
• Syncing to the backend when back online

I know browser security prevents sending SMS directly, so:

• Is using sms: URI a reliable fallback?
• Is Background Sync reliable enough?
• Would something like Capacitor help if we want native SMS access?

Would love to know how the team is thinking about this problem.

[Ankit-Basu]

Great question! In SheShield, we faced this exact challenge while designing the emergency SOS system.

✅ Here's our current hybrid approach:

1. Offline Triggering:

   • We save the event in IndexedDB with coordinates and timestamp.

2. SMS Fallback:

   • We use window.open("sms:+911234567890?body=Emergency%20Help!") to launch the device’s messaging app. This works well on most mobile browsers but not on desktop.

3. Background Sync:

   • We register a sync event in the service worker to send the event once the user comes back online.

4. Future Scope:

   • We’re exploring a Capacitor-based shell to access native SMS APIs, which would bypass browser limitations and support full offline functionality.

[ankan123basu]

Thanks for this amazing project! I'm looking into possible ways to trigger SMS in PWAs, and window.open("sms:") seems like a decent fallback on mobile.

I'll try exploring more and share if I find any useful tricks.