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Comment by bsagdiyev | Hacker News Reader

I feel like you’re being obtuse. They would need to verify that the call can be made and make it out the phone to the network, not actually make the call to a 911 operator. This can be part of an automated test suite even. Just ensure specific phone numbers cannot be intercepted by applications and diverted.

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@nikanj since I can’t reply directly to you. I would say you don’t worry about that, what purpose does your app have intercepting it? It should be something that the OS picks up on, and handles. If you are writing a dialler, you should be confident when you hand it off to the OS that it won’t pass it along to another app. I’m not sure why the radio portion is relevant when the issue is that Teams intercepted the call and caused it to fail. It never made it off the phone.

> If you are writing a dialler, you should be confident when you hand it off to the OS that it won’t pass it along to another app.

I've no idea how exactly this bug happened and therefore whether the following has any relation to that issue or not, but if you want VOIP apps and similar things to work, you do need to allow the "I've got a phone number and I want to place a call" step to be intercepted, because otherwise how are you supposed to make a call via VOIP etc. when selecting a number from your contacts list, a phone link in a browser, etc. if that step was hardcoded to the regular phone app?

There's a difference between a phone call, and an emergency phone call. The documentation for the ACTION_CALL intent even says that emergency calls won't work for the intent.

Android already differentiates between normal calls and emergency calls. Normal will be intercepted, emergency shouldn't be. And an emergency call is required to still work even if a SIM card is not present in your device.

You're assuming Android devices have cellular modems. Tons of Android devices do not have cellular modems. Think tablets, desk phones, etc.

No, I'm not. Android's documentation says it handles emergency calls through a separate workflow. The law requires Android to handle emergency calls through a separate flow. Neither of those things is predicated upon a cell connection.

Emergency is required to work a certain way, by law, and is documented to work that way, but didn't happen in the case of this bug. The OS is responsible for emergency calls, the dialler, which may be third party, for normal calls.

How do I, an lone app vendor, verify that my call makes it out of the phone, or abort it without 911 noticing a dropped call? The radio+network part is a black box from my perspective

PS: At least where I live, emergency services will show up at your house if you make a few 0-second 911 calls

You can contact your 911 call center through a non emergency line (numbers available here when you enter your state/region: https://www.nasna911.org/contact-911). You can then call and set up a time window for outbound test calls to be placed where they won’t send emergency services.

I've worked on some custom Android firmwares before, and I did this for our releases. It's easy, the 911 call center doesn't mind (it's scheduled beforehand), and it ensures that the phone can dial 911. If you can't manage to test emergency calls, don't release phone software.

If you can't test this, don't make a call-hijacking phone app. Simple as that!

Yes, that's the clear and obvious answer. We have regulations around things like being able to make 911 calls for a reason, because it's literally a life and death issue. Nobody should be making or selling a call-hijacking app if they can't perform even the most basic level of testing to ensure 911 calls still work.

You call the PSAP's non-emergency number and ask to schedule a few test calls. If you don't know how to reach them, call your local police non-emergency number, they'll be able to put you in touch.

You're supposed to do this when setting up new VOIP service too, to make sure location information is reported correctly. It's quite a normal thing and they're not at all surprised by it.

I would go so far as to say there are 2 types of phone people: Those who've placed a lot of 911 test calls, and those who're placing their users at risk.

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