A strange siren noise which woke up residents near Heathrow Airport has had social media buzzing.
The mysterious droning sound started after midnight on May 24 and lasted for at least an hour.
Sleep-deprived Twitter users from Stanwell and Ashford, next to the airport in Spelthorne, Surrey, were concerned that the ominous sound heralded nuclear attack.
Others suggested, more realistically, that the noise was coming from a nearby fuel depot.
It is a theory which Surrey Police seemed to favour. A spokesperson said they received six or seven calls between 1.30am and 2.30am and countless more messages from social media users.
She said: “The noise seems to have been coming from the direction of the fuel depot in Bedfont Road in Stanwell. We've contacted the depot but have yet to hear back.
"It was a siren noise more than an alarm and it’s not really a police matter but we know there was lots of social media about it.”
Others tweeted they could hear the siren from Feltham , and believed it to be from the young offenders' institute.
In the end, one user on Facebook appeared to have cracked the conundrum.
Shamus Doherty said a neighbour had received an email from Met Police which read: "I am unaware of the alarm myself so have contacted the oil terminal.
"Last night there was a false alarm at the terminal. This alarm sounded for longer than is usual and I understand this is being addressed.
"Apparently if you are a local resident you may well receive information/an apology about it in due course from the terminal."
Esso has confirmed the siren was at its Stanwell depot. So now we know.