There was no fire and it is believed the sensors were triggered by work being carried out overnight.
Security staff cordoned off parts of the building as a precautionary measure, amid fears toxic substances such as asbestos could have been released, but the all-clear was given shortly after 8am.
A Commons spokesman said the smoke detectors were activated in the early hours of Friday morning after overnight works in the basement. "While the alarms were being investigated, and as a precautionary measure, certain areas of the Palace were closed," he said.
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