“Arc has been stopped by iOS, and its requests to be restarted have been unsuccessful. Relaunch the app now to avoid unwanted data gaps.”

I’m constantly getting this error unless I have the app actively running. No other life tracking app I use (Welltory, Gyroscope, Swarm, Day One) has this issue. I don’t like having to keep an app open just to use it in the background. I don’t understand why it can’t just run as a background process like its peers.

(iOS 16.1, iPhone 14 Pro Max)

Hi @rolandsmash!

All location recording apps on iPhone must be alive (ie not swiped closed) in order to record location. iOS does not store any location data for later retrieval, so if an app is not alive at the time, it gets no location data and can’t fill in that gap.

Arc (and other apps) can partially get around being swiped closed by using various tricks to get automatically relaunched in the background. But there will be always be minutes or hours of delay between the app being swiped closed and the app being automatically relaunched, during which time there will be a gap in the location data.

The other apps you mention mostly don’t record constant location data, instead relying on only periodic “significant location change” location updates, which are typically 15 minutes or longer apart, and often hours apart. Gyroscope does attempt to do constant location data recording, which means it suffers the same as Arc when swiped closed, and either has to hope for a quick auto relaunch or has to fudge the data in the UI and hope you don’t notice the gap.

Most location recording apps intentionally rely only on location data with significant gaps between samples (minutes or even hours), and present the data in their UIs in such a way as to gloss over the gaps. Arc however is designed to record the highest detail, and doesn’t attempt to fake over any gaps (with the exception of gaps within a single visit, such that the gap started after arriving and ended before leaving).

So in short: Don’t swipe the app closed. And as a general rule of thumb, don’t swipe any apps closed. On average it won’t save you any battery, and in fact will end up costing you more battery life.

When you swipe an app closed, and it is then automatically relaunched (or relaunched manually by you) the app has to repeat its energy expensive launch cycle each time. By swiping apps closed from the app switcher, typically you will be shortening your phone’s battery life each day rather than extending it.

Instead if apps are left alone in the background, they will either go into a fully suspended state where they consume no energy at all, or will quietly do their work in the background while consuming very little energy. Then when the app is brought back into the foreground it doesn’t incur a repeat of its energy expensive launch time processes.

The most energy consuming part of any app is its time in the foreground, powering the screen’s brightness, and using energy to update its UI. When apps are in the background they consume orders or magnitude less energy. In Arc’s case, a few minutes of foreground time consumes about the same amount of energy as several hours of background recording.

If Arc is left in the background, it can continue recording for 24+ hours on a single charge, and on larger/newer phone models possibly can even beat 48 hours of constant recording on a single battery charge.

Anyway, either way, if you swipe the app closed you will get data gaps, and the same is true for all location recording apps.

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First of all, thank you for this amazingly thorough and informative response. I really appreciate it.

Secondly, I absolutely love this app. I mainly close out apps because I don’t like the clutter of leaving them open; however, if leaving Arc open is the only way to ensure its maximum functionality, then I will leave it open from now on.

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I’ve been using Arc for several years (I have continuous tracking data going back to 2013 when I originally used the Moves App and then imported it to Arc when Moves shut down).

I find Arc stays active in the background much longer if the phone is not being charged. I only charge the phone when I’m stationary for a while. That way, any data gaps are inside the location where it doesn’t affect the trip data. I check that Arc is running before setting off again, to avoid missing anything.

Since about iPhone 11, battery consumption has not been so much of an issue. Arc usually consumes between 4 and 10% overall. Looking at the Battery Settings right now, Arc has been running in the background for 22 hours!

I have one of my signature way-too-long explanations for this :joy:

Apps (and iOS itself) act differently when plugged in or running on battery. When the phone is plugged in, iOS (and some apps) will start doing various energy intensive daily housekeeping tasks, such as running backups, tidying databases, processing data, updating ML models, all sorts.

These days there’s a proper system for scheduling these tasks, which Arc uses. The tasks are registered with iOS, flagged as “needing power” (ie only to be run if the phone is plugged in), and requested to be run some period of time in the future. Then when the phone is plugged in iOS will start considering all those scheduled tasks and running them (if it feels in the mood).

Though Arc doesn’t want its own scheduled housekeeping tasks to be run while you’re travelling and data is being recorded. So if iOS starts up any of Arc’s scheduled tasks while you’re on the move, Arc will say “nah not now thanks”, and reschedule the task for later. But Arc can’t do that for the tasks scheduled by other apps, or iOS’s own housekeeping tasks. So there’s potentially a bunch of processing tasks firing up, doing various things, making the phone hotter and busier, while Arc is trying to record data.

An extreme situation of this kind is CarPlay / phone plugged in to car. Arc will be trying to record data while travelling, there might be a live navigation session (eg Google Maps or Apple Maps), perhaps iOS also decides to run some scheduled background tasks (but let’s hope not - that would be terrible timing), and on top of all that the phone is getting cooked by the sun through the car windscreen, potentially overheating. It’s a mess.

My old iPhone 7s test device (that I recently retired to a drawer somewhere) had an almost dead battery which would get less than about 1 hour of battery life if I tried to use the phone. But if I left the phone alone, not trying to use it at all, Arc would continue to record in the background uninterrupted for maybe 24 hours on a single battery charge.

The battery couldn’t even manage an hour of normal use, but for Arc recording in the background it could still easily eke out a full day of recording. Not exactly useful for a phone that anyone would want to use, but a useful example of how much difference there is between the energy consumption of actively using a phone versus the energy consumption of apps quietly doing their thing in the background.