Emergency calls

The short version

Dial 911 from any handset and the call leaves by the provider that holds the house’s registered emergency address. If that provider cannot carry it, the call tries every other provider in turn. If nothing can carry it, you hear a busy tone rather than silence, and that tone means reach for a mobile.

The rest of this page is the reasoning, because on this one subject the reasoning is the feature.

What the house does

The designated trunk goes first, unconditionally. With one provider there is nothing to decide. With more than one, trunks.toml names which carries 911, or the primary line’s provider does by default, and doorman check prints which it is and whether that was chosen or inferred, every time it runs and every time the daemon starts. Unset is never undefined, and a configuration with no answer for 911 refuses to render at all.

Nothing asks the trunk whether it is up. It is tried. A provider that does not answer a health check can be working perfectly, and diverting an emergency call off the one trunk whose address is on file, on a false alarm, at the worst possible moment, is exactly the failure this design exists to prevent. A trunk that is really down fails in milliseconds, and the call moves on.

Then every other trunk, best evidence first. Providers that declare a registered address are tried before ones that say nothing, and a provider that declares it has no emergency service goes last. The dispatcher may then see the wrong address, which is genuinely bad; a connected call lets a person say their address out loud, and a failed call gives them nothing. Connection first.

The call never borrows another line’s number. Emergency addresses are registered against a specific number, so 911 always leaves as the trunk’s own number and never as a second line whose address is somebody else’s house. The outbound console that lets a handset call out as another of your numbers cannot reach 911 at all, by where it lives in the dialplan and by refusing the number itself. Two independent things have to be wrong.

Bedtime does not apply. A handset under curfew can still dial 911.

What you have to do

1. Register the address with your provider. It is a couple of dollars a month and the one line item on a house phone worth never skipping. The providers page lists the charge for each.
2. Say what you know. In trunks.toml, e911 = true or false per provider. doorman check reports “unknown” rather than guessing when you have not.
3. Verify it the provider’s way. Most have a test procedure that does not involve calling 911. Use it after any change to numbers or providers.
4. Reject a provider without it. Not every provider offers emergency service in every area. One that does not means a phone that cannot call for help, which is a reason to choose a different provider, not a line to skip.

Be plain about this

This is a supplementary phone. It stops working in a power cut and on a bad internet day. It should never be a household’s only route to emergency services. Keep a mobile in the house and teach everyone, children included, that it is the one to reach for first. That is not a disclaimer; it is the accurate description of a hobbyist phone on a consumer internet connection.