IMO you're overangsting on what was the cause on this entire thing, and perhaps might be better served by focusing on what you would do differently if you ever experienced a fire alarm again - such as putting on your shoes

The front desk clerk might have been told it was a bedroom, and it was only after you checked out that she might have been told it was a conference room, which you found out when the hotel got back to you at a later date. I'm still boggled by you actually contacting them to find out what happened. I'm in the who cares camp. If it was a fire I'd obviously know; if it wasn't, then I don't care what caused it, just let me get back to sleep. I'm sure neither the contractor nor the hotel anticipated the accumulating dust to an extent that it would trigger an alarm, and yes it would be a 3rd party - ie, the refurbishment contractor.

In the case of a fire alarm, a hotel is always (properly IMO) going to err on the side of caution re: its guests & evacuation. Sorry you were inconvenienced, but would you really want to be in a hotel that decided to check things out before contacting the fire dept while possibly a real fire is happening & spreading? And btw, they can spread pretty quickly.

As far as I know, most hotel alarm systems are tied into the closest fire station when alarms are tripped. I don't think it requires a manual call, although that might be a back-up. Also, when a fire alarm goes off it goes off because the sensor thinks a fire IS occurring & something, regardless of what it was - real or dust, triggered the sensor. Once the fire dept is involved they have to do the sign-off on folk back into a building.

I'm now waiting for a thread that says the fire alarm went off & the hotel didn't evacuate the guests, putting us in potential jeopardy, should I ask for compensation or sue them

Again, be glad it wasn't a real fire, be glad it wasn't winter, and just move on.

Cheers.