Apps and PWAs for field work
No signal, with gloves
and in direct sunlight.
An app that only works on wifi and indoors is no use in a pen, on a building site or in a warehouse. We design for the worst case, and that changes concrete decisions: what gets downloaded in advance, how big a button is and what the contrast is measured against. Verified by measuring, not by opinion.
The three real conditions
Designed for the worst case, not for the demo
A demo is done sitting down, on wifi, looking closely at the screen. Real work is not. These three conditions are not edge cases: they are the normal scenario.
No signal
Not «with intermittent connection»: with nothing. The app installs and fully reloads with the network cut, and that is checked on every deployment, not once on day one. Whatever is needed outside is decided and downloaded beforehand, because out in the field it is too late to ask for it.
With the screen in the sun
The light grey on white that looks elegant in an office vanishes at midday in July. There is a high-contrast mode, and contrast is verified against the real composited background —the one produced by stacking translucent layers— not against the nominal colour, which is how contrasts get approved that later cannot be read.
With gloves and in a hurry
A 30-pixel touch target works with the clean finger of whoever coded it and fails with a work glove. Eleven screen sizes are verified: zero overflow, zero text below 11 pixels and zero touch targets smaller than 40.
What gets measured, and with what number
«Accessible» and «responsive» are things anyone says. These are the checks that run, with their threshold, and that fail the deployment if they break.
11
screen sizes verified, with zero overflow
11 px
the smallest text; nothing below
40 px
the smallest touch target; nothing below
WCAG AA
contrast against the real composited background
And the check that matters most: the app fully reloads with the network cut, verified on every deployment. Not once at the start, when everyone still remembers.
Frequently asked questions
PWA, offline and what to decide first
What is the difference between a PWA and a native app for field work?
A PWA installs from the browser, updates itself and does not depend on anyone approving a version in an app store — which in a company with fifty operators is the difference between fixing a bug today or next week. A native app wins when deep device access is needed: an industrial code reader, near-field communication or specific sensors. For most field work, the PWA comes out better.
What exactly does «works offline» mean?
That the app starts and fully reloads with the network cut, not that it holds out for a while on what it had in memory. The difference shows when someone closes the app in a basement and opens it again: if it was badly built, that is where the blank screen appears. We check it automatically on every deployment.
How do you verify it can be read in sunlight?
By measuring contrast against the real composited background, that is, the colour produced by stacking every translucent layer beneath the text. It is a detail almost nobody checks: measure against the nominal colour, it passes in the spreadsheet, and then out in the street it cannot be read. There is also a high-contrast mode the user can switch on.
Why 40 pixels of touch target and not less?
Because that is the threshold below which failures start with a thick finger, a glove or movement. Whoever codes the screen tests it sitting down, with a clean hand and looking closely: in those conditions a 28-pixel button seems enough. In a warehouse, it is not.
Can work done offline be synchronised?
Yes, and it is the part that needs most care. Whatever is recorded out of coverage is stored on the device and uploaded when the network returns, resolving what happens if someone touched the same record meanwhile. That decision —who wins in a conflict— has to be taken explicitly at design time, not left to whichever arrives first.
Has anyone tested your app where it actually gets used?
Not in the office: in the pen, on the site or in the warehouse, with gloves and no signal. That is usually where the real problems show up.
Tell us your case