Are the alarms actually still firing? I’d have expected them not to, since in the absence of a network the Roam can’t tell the time. 

The Sonos controller app is unable to configure the Roam over Bluetooth.

That is exactly what I would have said and expected, but on a brief test with a Move it did fire, albeit with the chime.

Maybe I did something wrong in the experiment 

Interesting. Presumably a rebooted device would eventually lose track of the time without a network connection. 

That’s interesting.  I can see why you would not want the alarm while in bluetooth mode, as there is a good chance you’re away from home and there’s no known way to turn it off.  On the otherhand, in case of a power outage, network outage, or simply forgot to take Roam off bluetooth mode while at home, you would still want the alarm to go off as normal.   Indeed old style clock radios had a battery back for when the power went out.

Might be good idea for Sonos to have a setting for how the alarm should function while in bluetooth mode, so you can at least choose the behavior you want in advance.

In answer to the earlier question, it was the chime alarm that was going off.  Not what I wanted when on vacation.

Here is a possible way to get rid of the alarm. 

1. On one of the phones in your party, set up a mobile hotspot with the same SSID and password as your home router (if you can remember them)

2. Your phone and Roam should now connect to the mobile hotspot. 

3. Now that you are in WiFi mode, disable the alarm.

No promises. If you are able to do it, it may or may not work.