What is offline mode / PWA?
Offline mode means your app continues to work — at least partially — when the device has no internet connection. Data entered offline is queued and synced when connectivity returns. For a field worker in a mobile dead zone, this is the difference between a usable app and an unusable one.
PWA (Progressive Web App) is a related concept: a web application built with technologies that allow it to behave like a native app — installable on the home screen, working offline, receiving push notifications — without going through an app store. PWAs are increasingly popular for businesses that want app-like behaviour without the cost and friction of separate iOS and Android builds.
They're often implemented together, but they're distinct: offline mode can be added to a native app, and a PWA can have varying degrees of offline support.
When does your app need it?
- Your users work in areas with unreliable connectivity — rural properties, construction sites, basement carparks, field locations
- Data collection or job completion can't wait for signal — forms, signatures, photos, notes
- You want to reduce app store friction — PWA installation is faster and doesn't require approval
- Your app is used by trades, agriculture, logistics, or any field-based workforce
- You want to reduce server load — some data can be served from the local device cache
- Performance matters: caching assets locally makes the app feel significantly faster on repeat visits
How much does it cost?
Adding offline mode or PWA capability typically adds 11–21 hours of development — roughly $2,000–$5,000 AUD.
The range reflects what "offline" actually means for your app:
Basic offline (lower end): The app loads and displays previously-fetched data without internet. New actions are blocked until connectivity returns.
Full offline-first (higher end): Users can complete core workflows — fill forms, take photos, capture signatures — and everything syncs intelligently when they reconnect. Conflict resolution (what happens if two people edit the same record offline) adds the most complexity.
PWA-specific work — service worker setup, manifest, install prompt — typically adds 6–10 hours on its own.
How it's typically built
For web apps / PWAs: A service worker (a background script in the browser) intercepts network requests and serves cached responses when offline. IndexedDB stores data locally. When connectivity returns, queued changes are synced to the server.
For React Native apps: Libraries like WatermelonDB or a local SQLite database store data on the device, with a sync layer that pushes and pulls changes when online.
The hard part isn't storing data locally — it's sync conflict resolution. If two users edit the same record while offline, the app needs a strategy for which version wins, or how to surface the conflict to a user.
Australian construction and field service businesses are the most common requesters of this feature — ELMO, ServiceM8, and Fergus all have offline-capable mobile apps because their users (tradies, inspectors, site managers) frequently work in low-signal environments.
Questions to ask your developer
- What specifically works offline? Get a list. "Offline mode" can mean anything from "the app loads" to "everything works exactly as online." You need agreement on scope.
- How does sync conflict resolution work? If two users edit the same job while offline, what happens when they reconnect?
- How much data is cached locally? Caching everything may be impractical for large datasets — understand what the trade-off is.
- For PWAs: what are the limitations on iOS? Safari has historically had worse PWA support than Chrome on Android. Test on iOS Safari specifically.
- How are background syncs triggered? Does the app sync immediately on reconnect, on a schedule, or only when manually triggered?
See also: Real-time updates · Background & scheduled jobs · App cost calculator