Four fire engines and an extension ladder were rushed to a multi-storey block of flats in Preston city centre after a fire alarm went off and automatically alerted Preston Fire Station.
But when the firefighters arrived at the six-storey Room Apartments on Lawson Street, it quickly became clear there was no blaze.
The smoke alarm, believed to be particularly sensitive, had seemingly been sprung after some kind of incense burner wafted smoke into one of the corridors.
Firefighters received the call at 12.50pm today.
There is still a high alert over high rise blocks following the Grenfell Tower tragedy in London back in June.
Fire crew manager Chris Wales said: “We sent four fire appliances and the ladder in response to a potentially serious blaze at a multi-storey housing block.
“However, we fairly rapidly realised what had happened by the smell and the sort of haze we found in the corridor.”