Does GPS tracking work with the screen locked?

The short answer

Locking the screen does not, on its own, stop a GPS recording. iOS suspends most apps the moment they leave the foreground, but a location-tracking app is a deliberate exception: one that has been granted background location access keeps receiving GPS updates with the screen off or another app open, which is why the status bar shows a small indicator whenever something is using your location in the background. If that indicator appears when you lock the screen, the recording is still running.

What ends a recording early has almost nothing to do with the lock screen itself, and almost everything to do with three other things: which location permission the app was given, whether it was force-quit, and whether the battery ran out.

The permission that actually matters

iOS offers location access on a spectrum, and for a hike recorded over several hours the relevant choice is between "While Using the App" and "Always". An app limited to "While Using the App" is expected to lose location updates once it has been backgrounded for a while, because that is what the permission means — iOS is only guaranteeing access while the app is the thing on screen. "Always" is what tells iOS to keep servicing that app's location requests regardless of what is on screen, which is the setting a tracking app needs to survive a phone going in a pocket for a few hours.

This is worth checking once, in Settings → Privacy & Security → Location Services → the app in question. If a recording has come back with missing sections before, this is the first place to look, not the app itself.

What force-quitting actually does

Swiping an app away in the app switcher does not put it to sleep — it ends it, along with anything it was doing in the background, GPS recording included. That is different from simply locking the screen or switching to another app, both of which leave a properly permissioned app running underneath. If a recording has stopped partway through and there is no prompt to resume an unfinished route, it is worth checking whether the app was closed from the app switcher along the way, which is an easy thing to do out of habit while closing everything else.

Low Power Mode and Background App Refresh

Two other settings get blamed for the same problem and are usually not the cause. Low Power Mode reduces background activity for things like mail fetching and app refresh, but an app running an active, foreground-started location session — the kind a recording app runs from the moment you press start — is not the activity Low Power Mode is built to interrupt. Background App Refresh, a separate toggle that lets apps update their content while unopened, is also a different mechanism from a live GPS session, and turning it off does not end a recording already in progress.

Neither setting is irrelevant to battery life over a long day — screen time and a cellular radio searching for coverage generally matter far more — it is only that neither one is the likely explanation for a recording that stopped.

If a recording does get interrupted

Phones die, apps occasionally get closed out of habit, and there are edge cases outside any of the above. A recorder worth trusting on a long day should assume this happens sometimes and make the failure recoverable rather than silent, rather than assuming the ideal case will always hold.

What TrailCam does

TrailCam keeps recording with the screen off or while you are in another app, and pausing or resuming is always something you do deliberately rather than something the app guesses at from your speed. If a recording is ever interrupted mid-walk, TrailCam offers the unfinished route back the next time you open it, rather than losing it outright. It is free to download.