Low Data Mode and Data Saver, explained: what they actually turn off
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Most phones ship with a single toggle that quietly cuts data use without you changing a single habit: Low Data Mode on iPhone, Data Saver on Android. Our guide to using less data abroad mentions flipping it on as one line in a longer list, but it's worth its own explanation, because it doesn't just throttle everything evenly. It turns specific things off for specific apps, and knowing which ones changes whether the switch is a free win or a mild annoyance on your trip.
What Low Data Mode actually does on iPhone
With iOS 13 and later, Low Data Mode restricts background network use rather than slowing your connection down. Apple documents the general behavior as: apps stop pulling network data when you're not actively using them, Background App Refresh turns off, streaming quality drops, and automatic downloads and backups pause. A few built-in apps adapt in specific ways worth knowing before you rely on them abroad:
- App Store: turns off video autoplay, automatic app updates, and automatic downloads.
- Music: turns off automatic downloads and high-quality streaming.
- Podcasts: limits how often shows refresh, and only downloads new episodes on Wi-Fi.
- News: turns off article prefetching, so stories load a beat slower when you tap them.
- iCloud: pauses automatic backups and iCloud Photos updates.
- FaceTime: lowers video bitrate to fit a slower connection.
Turning it on for just your travel eSIM line
The part most people miss: on a dual-SIM iPhone, Low Data Mode isn't all-or-nothing. Go to Settings → Cellular (or Mobile Data), tap your travel eSIM's line specifically, then turn on Low Data Mode there. That applies the restrictions only to the line carrying your travel data, your home SIM, if you keep it active for calls and texts, is untouched. This is the version worth setting up before you fly: it means you get the savings on the line where they actually matter, without changing how anything behaves on your regular number. If you haven't set the two lines up yet, our dual-SIM settings guide walks through which line should carry calls versus data in the first place.
What Data Saver does on Android
Android's equivalent works a level up. Google's own Data Saver documentation describes it as a system-wide setting under Settings → Network & internet → Data Saver: once it's on, most apps can only fetch background data over Wi-Fi, while whatever app you're actively using still gets mobile data normally. Samsung's version sits under Settings → Connections → Data usage → Data saver and works the same way. Unlike iPhone, there's no separate toggle per SIM, Data Saver applies to whichever line is currently set as your mobile data line, which for a travel eSIM should already be the eSIM itself. If an app misbehaves with it on (a messaging app delaying notifications, for example), both versions let you flip that one app to unrestricted: iPhone doesn't offer per-app exceptions the way Android does, but Android's Unrestricted data list (under Data Saver) lets you keep specific apps exempt while everything else stays capped.
| iPhone Low Data Mode | Android Data Saver | |
|---|---|---|
| Where it's set | Settings → Cellular → [your line] | Settings → Network & internet → Data Saver |
| Per-SIM on dual SIM | Yes, pick the line | No, applies to your data SIM |
| Per-app exceptions | No | Yes, via Unrestricted data |
| Streaming quality | Reduced automatically | Depends on the app's own setting |
| Background sync (e.g. photo backup) | Paused | Wi-Fi only |
The trade-offs worth knowing before your trip
None of this is free. The apps built to lean on background data will feel it:
- Photo and video backups (iCloud Photos, Google Photos) pause until you're back on Wi-Fi, so your camera roll fills up rather than syncing as you shoot.
- Some messaging and email apps check in less often in the background, so a new message can arrive a little late until you open the app.
- Streaming video and music default to a lower quality tier, worth a manual bump if you're on a generous plan and want the difference.
- Maps apps may prefetch less of the route ahead, so downloading offline map areas before you go still matters even with this on.
Your Zwitchy usage alerts at 80% and 100% keep working regardless of these settings, they're based on what the network reports for your plan, not on anything happening in Low Data Mode or Data Saver. Turning either on just means you're less likely to hit those thresholds in the first place.
Should you turn it on for the whole trip?
If you bought a generous plan and want video and photos to just work, skip it, that's exactly what the extra gigabytes are for. If you're stretching a smaller plan across a longer trip, or you're not sure yet how much data you'll actually need, turning it on for your travel eSIM's line from day one costs you almost nothing in practice and buys real headroom. It's also the easiest thing to reverse if you notice a specific app struggling, flip that one line, or that one app on Android, back off rather than abandoning the setting entirely. And if you do end up close to your limit anyway, a top-up attaches instantly to the same eSIM with no reinstall needed.
A common pattern: someone buys a 5 GB plan for a two-week trip, turns on Low Data Mode for the eSIM line at the airport, and barely notices it's on beyond photos taking a moment longer to finish uploading once they're back at the hotel Wi-Fi. That's the setting working as intended, it doesn't make maps slower to load or messages stop arriving, it just defers the background work that was never urgent in the first place until you're somewhere it's free to do.
For a fuller picture of where your data actually goes day to day, our guide to how much data your apps really use breaks it down by activity, and checking your eSIM's usage tells you whether either setting is making a visible dent.
Does Low Data Mode or Data Saver block calls or texts?
No. Both only affect data used by apps in the background. Calls and texts on your home SIM, and voice/video call quality on an active call, aren't touched.
Will I miss notifications with these turned on?
Rarely, and usually only a short delay for apps that rely on frequent background refresh. If one specific app lags, add it to Android's Unrestricted data list; on iPhone, turn Low Data Mode off just for that line if it becomes a real problem.
Can I turn on Low Data Mode for my travel eSIM without affecting my home SIM?
Yes, on iPhone this is per-line. Go to Settings → Cellular, tap your travel eSIM specifically, and turn Low Data Mode on there. Your home SIM line is unaffected.
Does Android's Data Saver work per SIM like iPhone's Low Data Mode?
Not quite. Data Saver is one system-wide toggle, and it applies to whichever line is currently your mobile data line. If your travel eSIM is set as your data SIM, that's the line it restricts.
Will turning these on stop Zwitchy's data usage alerts from working?
No. Those alerts are based on usage the network reports for your plan, not on anything tracked locally by Low Data Mode or Data Saver, so you'll still get warned at 80% and 100%.
