Guests in bathrobes were forced onto Brighton seafront after a fire alarm went off at the Grand Hotel.
About 30 people - some of whom had been enjoying a sauna - waited outside for 30 minutes as firefighters searched the building one room at a time.
A faulty alarm had sparked the evacuation, which began at about 7.37pm yesterday.
Brighton Fire Station crew manager Steve Liszka said: "The alarm was going off but there was nothing to show what it was, so we had to search the entire building.
"Luckily the staff had had their fire marshalling training in the day, so they were up to speed with what to do."
Less than an hour before, customers at Asda's Hollingbury store were evacuated when the shop's sprinkler system went off.
A forklift truck had accidentally broken a pipe, which triggered the alarms at the Crowhurst Road shop.
Customers spent at least 15 minutes waiting for the go-ahead to return to their shopping.
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