local network alert with cellular data?

I have a local network alert with cellular data.

That seems… well… unlikely. WWANs are explicitly excluded from local network privacy, as discussed in Local Network Privacy FAQ-1.

It’s more likely that some subsystem within your app is trying to use the Wi-Fi interface even though the device has WWAN as the default route. Tracking that down can be quite tricky. Presumably you didn’t write code to do this, in which case it’s most likely some third-party library you’re using. My experience is that third-party media sharing libraries are the most common cause of this. Do you have anything like that in your app?

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Quinn “The Eskimo!” @ Developer Technical Support @ Apple
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In the case of WWAN, the use of the Wi-Fi interface will also trigger the local network alert?

It can. Keep in mind that “the phone is on cellular” doesn’t mean that the phone is only using WWAN. Rather, it means that phone is using WWAN for the default route. Unless you turn Wi-Fi off, Wi-Fi is always active. At a minimum it’s scanning for Wi-Fi networks to join but, even when it’s not on a network, you can connect using peer-to-peer Wi-Fi. So it’s perfectly feasible for the local network privacy alert to pop up while the phone is using WWAN for the default route.

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Quinn “The Eskimo!” @ Developer Technical Support @ Apple
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I want to discover caller by breakpoint

That’s not possible in the general case. The problem is that the local network privacy alert can be triggered by a variety of different mechanism. Some of these you can find with a breakpoint but some of them are the result of operations within the kernel (for example, if a packet your app sends ends up being routed to a local interface).

I’ve helped developers with problems like this in the past and I recommend:

1. Start by auditing your own code for stuff that’s likely to trigger this.

2. If you don’t find anything, then start removing third-party libraries until the problem goes away.

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Quinn “The Eskimo!” @ Developer Technical Support @ Apple
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it happens once in a while

Bummer. Unfortunately that makes things too tricky for me to handle here on DevForums. I recommend that you open a DTS tech support incident so that either Matt or I can allocate time to look into your issue in depth.

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Quinn “The Eskimo!” @ Developer Technical Support @ Apple
let myEmail = "eskimo" + "1" + "@" + "apple.com"