What an "offline PDF scanner" actually means

Three different claims wearing the same word

When an app says "offline", it is making one of three claims. They are independent: an app can satisfy any one of them and fail the other two.

The first is about availability. The app keeps working on a train, in a basement, on a flight. This is a convenience feature and says nothing about where your documents go — an app can work offline and sync everything the moment the signal returns.

The second is about your documents. The pages are processed on the phone and are not uploaded. This is the claim that matters for a contract or a medical report, and it is the one most rarely stated plainly.

The third is about identity. There is no sign-up, no email, no login, so nothing you scan is attached to an account that outlives the install. An app can be account-free and still upload every page, and plenty are.

• Works without a signal — a convenience claim.
• Does not upload your documents — the privacy claim.
• Needs no account — an identity claim, separate from both.

The airplane-mode test

You do not need the source code to check the second claim. Cut the network and see what the app can still do. Anything that keeps working is running on your phone, because there is nowhere else for it to run.

Run the whole path you actually care about, not just the capture. Plenty of apps scan locally and then upload for OCR or export, so a test that stops at the shutter button proves very little.

Then read the Data safety section on the app's Play listing. It is a declaration the developer files with Google, and it has to name what the app collects and what it shares. An app that passes the airplane-mode test but declares that it collects "Files and docs" and shares them is telling you the upload happens later.

• Turn on airplane mode and confirm Wi-Fi and mobile data are both off.
• Scan several pages and save the document.
• Run OCR, add a signature, and export or share the result.
• Note anything that spins forever or shows a network error.
• Turn the network back on and open the Play listing's Data safety section.
• Compare what the app could do offline with what the listing says it collects.

What ScanCrypt still sends with the network on

ScanCrypt passes the test above: every document tool works with the radio off. That is not the same as the app never talking to the internet, and pretending otherwise would fail the standard this page just set.

With a connection, the app sends: on the free tier, ads through Google AdMob, including the advertising ID. Crash reports and anonymous usage analytics through Firebase, and analytics can be switched off in Settings → Privacy & Data. Feature flags and pricing through Firebase Remote Config. No document content is included in any of it, and nothing goes to any AI service.

Three things genuinely need a connection, and none of them is a document tool. Ads will not load on the free tier, which costs you nothing but the banner space. Purchases go through Google Play, which needs to reach Google. Update checks go through Play as well.

Two tools in the catalog need the network by definition, because the network is the feature: Web to PDF fetches a page from a URL, and WebDAV Sync uploads a file to a server you nominate. Both are Pro tools, and neither runs unless you open it.

• Ads, on the free tier only — the app works without them.
• Purchases and restores, through Google Play.
• Update checks, through Google Play.
• Web to PDF and WebDAV Sync — network is what they are for.

What the test cannot tell you

Airplane mode proves that a feature can run locally. It does not prove that the app refrains from uploading once the signal is back, which is why the Play Data safety declaration is the second half of the check. Between the two you get a decent picture: what must be local, and what the developer has told Google they collect.

ScanCrypt is not open source, so this pair is the honest extent of what you can verify from outside. It is more than most scanner apps let you check.