What type of Notifications do you get on an iPhone when the Smoke Alarm goes off?

What type of Notifications do you get on an iPhone when the Smoke Alarm goes off? Is it a normal notification (i.e. soft 'ping' sound, or no sound at all during e.g. sleep mode), or is there a loud sound like an alarm clock or siren?

And does the app have a so-called 'critical notification' setting?

I think this is crucial to have if you are in a location where you can't hear the 85dB sound the device itself makes when smoke is detected.