Wi-Fi Assist and auto data switching: settings that quietly spend travel data
Some of the data a traveller doesn't expect to use is spent on purpose by the phone: it tops up weak hotel Wi-Fi with mobile data, or borrows the other SIM when one line is busy. Here is what each setting does and when to turn it off.
On recent iPhones, Wi-Fi Assist has been replaced by Connectivity Assist in Settings → Wi-Fi; Apple says it uses cellular data alongside weak Wi-Fi and may use more data. Allow Cellular Data Switching lets an iPhone use data from both lines. Android has similar options. On a trip, keep the travel eSIM as the only data line.
- Connectivity Assist (iPhone)
- Settings → Wi-Fi
- Replaces
- Wi-Fi Assist (was in Cellular)
- Not used when
- international roaming or Low Data Mode (Apple)
- Allow Cellular Data Switching
- uses data from both lines
- Pixel
- Automatic data switching
- Our travel setting
- switching off, travel line for data
On this page
Which settings move your traffic without asking?
| Setting | What it does | Travel risk |
|---|---|---|
| Connectivity Assist (iPhone, Settings → Wi-Fi) | Uses cellular data alongside Wi-Fi when Wi-Fi is weak, busy or not connected to the internet | Spends plan data in a hotel with poor Wi-Fi |
| Allow Cellular Data Switching (iPhone, dual SIM) | Lets the iPhone use cellular data from both plans, depending on coverage and availability | Data may run on the home line abroad |
| Automatic data switching (Pixel) | Lets the phone use the second SIM for data in some situations | Same as above |
| Switch to mobile data (Samsung Intelligent Wi-Fi) | Uses mobile data when the Wi-Fi connection is unstable | Spends plan data on weak Wi-Fi |
None of these is a bad setting. At home they make the phone feel more reliable. On a trip with a fixed amount of data, or with an expensive home line in the background, they can turn a careful plan into a surprise.
What is Connectivity Assist, and how is it different from Wi-Fi Assist?
Apple has renamed and moved the feature. Its help page says Connectivity Assist uses cellular data to improve your connection when Wi-Fi is slow or unusable, that it appears in Wi-Fi settings, and that it replaces and supersedes Wi-Fi Assist, previously found in Cellular settings. If Wi-Fi Assist was on when you updated, Connectivity Assist is on by default. Apple also says that with it turned on you might use more cellular data.
To change it: open Settings → Wi-Fi, make sure Wi-Fi is on, scroll down and turn Connectivity Assist on or off. Apple adds that you can turn it off for a particular network.
One detail helps travellers: Apple says Connectivity Assist isn't used when the iPhone is international roaming, in cellular Low Data Mode, or with some third-party apps that stream audio and video. Many travel eSIMs do connect as roaming, but you don't need to know which kind yours is. Low Data Mode on the travel line covers it either way, and it saves data elsewhere too.
What does Allow Cellular Data Switching do?
On an iPhone with two lines, you pick one for cellular data. Apple's Dual SIM page says that if you want the iPhone to use cellular data from both plans, depending on coverage and availability, you turn on Allow Cellular Data Switching. Apple also notes it is needed if you want to receive calls on your other number while on a call using the data line.
For a traveller, the home line is the other line. If switching is on and the home line's data roaming is on, some data could run on the home line, at whatever your home carrier charges abroad. The safe travel set-up is:
- Cellular Data: the travel eSIM.
- Allow Cellular Data Switching: off, unless you specifically need to receive calls on the home line during data-line calls and you accept the risk.
- Home line, Data Roaming: off.
- Travel line, Data Roaming: on, as most travel eSIMs need.
The home SIM guide has the full checklist for keeping your number reachable without roaming data charges.
What are the Android equivalents?
On a Pixel, Google's dual-SIM help describes Automatic data switching in Settings → Network & internet → SIMs. Google notes that receiving calls on both SIMs at the same time needs automatic data switching on for the second SIM, the same trade-off as on iPhone. Samsung phones have a data switching option in SIM manager and, separately, a Switch to mobile data option under Intelligent Wi-Fi in the Wi-Fi settings. For a trip, turn off both kinds unless you have a reason to keep them.
How much data can these settings spend?
There is no fixed figure; it depends on how bad the Wi-Fi is and what you do on it. As an illustration: if poor hotel Wi-Fi pushes an evening of video calls and streaming onto mobile data, the plan pays for that evening at mobile rates, from hundreds of megabytes for low-quality video to gigabytes for HD. On a small plan, that can be a day or two of allowance gone in one evening. That is the case for checking these switches before you go, not after.
How do I spot that it happened?
On iPhone, Settings → Cellular shows per-app usage for the period and Apple notes that Connectivity Assist can increase cellular use. If you see heavy use from apps you only used on hotel Wi-Fi, assist or switching is the likely cause. On Android, check the app data list for the travel SIM, and the home SIM's list, which should be close to zero abroad.
A one-minute check before you fly
- iPhone: Settings → Wi-Fi → Connectivity Assist off, or Low Data Mode on for the travel line.
- iPhone: Allow Cellular Data Switching off; home line data roaming off.
- Pixel: Automatic data switching off in Network & internet → SIMs.
- Samsung: data switching off in SIM manager, and Switch to mobile data off under Intelligent Wi-Fi.
Frequently asked questions
Where did Wi-Fi Assist go on iPhone?
Apple says Connectivity Assist now appears in Wi-Fi settings and replaces Wi-Fi Assist, which used to be in Cellular settings. If Wi-Fi Assist was on when you updated, Connectivity Assist is on by default.
Does Connectivity Assist work while roaming?
Apple says it isn't used when your iPhone is international roaming or in cellular Low Data Mode, among other cases. Whether a travel eSIM line counts as roaming depends on the plan, so turning on Low Data Mode is the surest way to keep it from spending data.
What does Allow Cellular Data Switching do?
Apple says it lets an iPhone use cellular data from both plans, depending on coverage and availability. It is also needed to receive calls on your other line while you are on a call on the data line.
Can I turn Connectivity Assist off for one network only?
Yes. Apple says you can turn it off for a particular network, which is useful if you want a specific Wi-Fi network to stay Wi-Fi only.
Got your number? Match it to a plan
On TripoSIM, choose your destination and compare total GB, validity, any daily full-speed amount and the Hotspot badge on each plan card.
We take data figures from the app makers' own help pages where they publish one, convert published bitrates with kbit/s × 0.45 = MB per hour, and label every planning assumption. We don't run paid reviews or publish prices. Editorial policy · How we get our figures · Who owns this site
Sources and how we checked
- Apple Support: About Connectivity Assist
- Apple Support: Use cellular data on your iPhone or iPad (Connectivity Assist, System Services)
- Apple Support: Using Dual SIM with an eSIM
- Apple Support: Use Low Data Mode on your iPhone and iPad
- Pixel Phone Help: How to use dual SIMs
- Apple Support: Use eSIM while traveling internationally
Figures were read from these pages on 7 November 2026. Apps change their settings and rates; if a number here disagrees with the app on your phone, trust your phone's own data counter. See how we get our figures.
Related reads
Home SIM plus travel eSIM: how to keep both without surprise roaming
How to keep your home number on while a data-only travel eSIM carries the data: which line gets data, data roaming switches and SMS, on iPhone and Android.
Read the guide →
What is "System Services" data on iPhone, and Google Play services on Android?
What "System Services" on iPhone and "Google Play services" or "Android OS" on Android mean in the data list, why they grow abroad, and how to reduce them.
Read the guide →
Android Data Saver for travel: the settings to change on Pixel and Samsung
The Android settings that cut travel data: Data Saver, background data per app, Play Store updates on Wi-Fi, data switching, with Pixel and Samsung paths.
Read the guide →