This is nasty. You need to interrupt power to all AC powered units in order to instantly mute the system. Portable units, such as ROAM’s and MOVE’s will care less about this power interruption. You could check with SONOS PROFESSIONAL and ask if they have any options.

A certified, professional alarm system will provide a signal that external systems can use to trigger their own shutdown when the alarm is tripped. An inspector will fake a fire and expect the music to stop as the alarm starts.

There are various schemes that could be used. The most obvious would be a power relay for each AC powered unit that is tied back to the alarm trigger. Of course this is useless for the portable units. Another scheme could use a bunch of smart outlets for the AC powered units.— but something would need to tell the outlets to shut down. An interesting DIY scheme could use a Raspberry Pi (or similar) to issue commands (individually) shutting down the SONOS units or their outlet. This could not be 100% reliable because it depends on network communication being available during the shutdown process.

Off Topic...somewhat….

​@buzz recommendation to contact Sonos Professional in spot on. However, when you click on the link you’ll notice that the Sonos speakers are in-wall, in-ceiling and outdoor. Those are wired solutions. The only non-wired speaker (so-to-speak) is the Era 100 Professional series. The catch being that it is PoE driven which stands for Power Over Ethernet.

There is a very good reason for using a wired solution in a retail setting. The human body acts like a sponge and absorbs radio waves of which Wi-Fi frequencies are included.  That’s not a reason to think that Wi-Fi frequencies are some sort of health hazard. The point I’m trying to make is that Sonos speakers communicating over Wi-Fi can be prone to losing connection when large gatherings of humans occupy a space, such as in a retail environment.

The speakers you have chosen are all wireless that must communicate over your establishments         Wi-Fi. Unlike previous Sonos speakers they cannot be wired back to a router to create what is called the SonosNet which isolates them from the standard 2.4Ghz Wi-Fi frequency. However, even so the SonosNet is still a wireless connection.

My intent has not been to “rain on your parade” but offer inciteful information.  

Cheers!