[bearbin]

There's a physical product that implements the same idea [1]. I'm not sure how it actually works (presumably there's a patent somewhere, is there an alternative solution?) but it's quite a magic feeling to hear the fire alarm go off and the doors independently close by themselves. If you're in a building that uses these, you can test yourself by playing a recorded fire alarm sound - they work on quite a few different ones (and it really doesn't have to be that loud!). They also have a surprisingly long battery life, ~10 years I think so the detection mustn't take much power at all.

[1]: https://www.fireco.uk/products/sound-activated/dorgard/

[paranoidrobot]

Ubiquiti also has a battery powered alarm-sound sensor in their Unifi Protect lineup[1]

> "Based on UL217 and UL2034 alarm patterns."

UL217 is apparently for smoke alarms, UL2034 is apparently for CO alarms.

https://store.ui.com/us/en/collections/unifi-camera-security...

[treflop]

You can also enable fire alarm audio detection on iPhones, HomePods and other home smart hubs.

[msla]

> it's quite a magic feeling to hear the fire alarm go off and the doors independently close by themselves

Closing doors on a fire alarm seems hilariously cruel.

[flyinghamster]

In many large buildings (schools, etc. in particular), you want the internal fire doors to close to keep the fire from spreading. Of course, exits must be provided for each isolated section.

[c22]

It prevents the fire from quickly moving through the building...

[msla]

Also, people.

[withinboredom]

The doors don't lock, they just close.

[zamadatix]

Yeah, that's a given, but the point of fire doors is to maximize overall survivability instead of the "average doors crossed per minute" stat in isolation.

[chedabob]

These are installed on doors that have an auto-closer anyway. They deter people from propping them open permanently with a wedge or a chair.