Most construction software treats "offline" as a degraded mode — something that just about limps along until you're back on 4G. On a real site that gets the order backwards. The plot with no signal isn't the edge case; it's Tuesday. So the question isn't whether an app survives being offline. It's whether the person holding the phone can tell the difference.
In DuoApp, the answer is no — and that's deliberate. A slow connection, a fast connection, or no connection at all produce the same sequence of taps and the same waiting time, because nothing the inspector does waits on the network.
Photos appear instantly
Tap the shutter and the thumbnail is there. Not "there once it's uploaded", or "there once it's been compressed" — there, immediately, before any processing has happened at all.
The compression and storage run behind you, on a background thread, while you carry on ticking off the next item. A modern phone camera produces a 5 MB photo; resizing that in the foreground is what makes other apps pause for a beat on every capture. On a forty-item sheet, those beats are the job.
The capture path
- The photo shows the moment the camera closes — no processing wait
- Scrolling and ticking stay smooth while it compresses in the background
- Nothing blocks on the upload, so signal strength never changes the pace
- Everything is held on the device until the server has confirmed receipt
The report is built on the phone
When a QC or aftercare report is finished, the PDF is generated on the device — photos, notes, checklist results, remedial work and the signature, laid out as a proper document. No server round-trip, so no signal required.
That matters because the moment you want the report is the moment you're standing in the plot, not two hours later at a desk. The photos are already on the phone; there's no good reason to need a data connection to arrange them into a page.
Email it from site, with no connection
This is the part people don't expect. Tap Email QC with no signal at all, and your normal mail app opens with the report already attached, the subject filled in and the project and plot in the body. Press send and the phone queues it, exactly as it would any other email, and it goes the moment you're back in coverage.
The client gets the report the same day. Nobody has to remember to do it later from the office.
Then it syncs itself
When signal returns, submissions and photos upload in the background — once, and only once. Every photo carries a stable key so a retry after a dropped connection can't produce a second copy, and a submission the server has already accepted is recognised rather than duplicated.
If something can't be sent, it says so plainly and keeps the work safe on the device until it can be. What it never does is quietly lose a photo and produce a report without the evidence in it.
DuoApp matches it offline — and builds the PDF on the device
Site Pro is a capable site-inspection app, and it's the one our customers most often ask us to match on offline working. Two behaviours in particular:
- Instant photos — the picture appears the moment you take it, with no processing pause. DuoApp does this.
- Email a report from site with no signal — the mail app opens with the report attached, ready to send, and queues until you're back in coverage. DuoApp does this too.
Where DuoApp goes further is how that report is produced: the PDF is generated on the phone itself — photos, checklist, notes, remedial work and signature — so a complete, sendable document exists before the device has spoken to a server at all.
And it's the same record either way. Once signal returns, the submission syncs into the same project, plot and audit trail as anything captured online, with no separate offline pile to reconcile.
Worth testing on both, on a real plot with the aeroplane on: take a photo, finish the report, and send it — all without signal. Book a walkthrough and use one of your own jobs.
The same for aftercare
Post-handover aftercare inspections work identically — the same instant capture, the same on-device report, the same email-from-site. Aftercare visits are often the ones furthest from a good connection, in occupied homes where you want to be in and out.
And it's all one record
Once synced, offline work is indistinguishable from anything captured online. It lands in the same audit trail, against the same plot and stage, with the same timestamps and attribution. There's no separate "offline" pile to reconcile.
The principle, again
Capture it once, at the source, and keep the trail — the idea that runs through the whole product. For inspections, it just has to hold when there's no signal for a hundred metres in any direction. That's the bar we built to.