The phrase "an alarming sight" is correct and usable in written English.
It can be used to describe something that causes concern or fear due to its appearance or nature.
Example: "The abandoned building, with its broken windows and overgrown weeds, was truly an alarming sight."
Alternatives: "a disturbing view" or "a shocking scene".
They presented an alarming sight.
In action, Mazie is an alarming sight.
Members of the English upper class wriggling to ragtime in evening clothes can be an alarming sight.
One Greek visitor to Gaul a few decades before Caesar's invasion reported seeing enemy heads regularly strung up as trophies outside Gallic huts – an alarming sight, he confessed, though in time one did get used to it.
Arsenal faded, and Mesut Özil's woeful defending for Everton's winner – backing away as Barkley's corner arrived at the penalty spot – was an alarming sight for a manager with designs on the title.
At the start of Louise Candlish's superb thriller "Our House," Fi Lawson, a 40-ish wife and mother, is returning to her comfortable home in South London when she is greeted by an alarming sight: Someone is moving into her house.
Despite the alarming sight of a plant surrounded by sandbag walls and a dozen pumps sucking in and spitting out water, Mr. Jaczko said later at a news conference that the operators had the situation in hand.
Jobless men were already roaming the roads, an alarming new sight for townspeople not used to such things.
I took a turn, but kept breaking out in a sweat and being greeted with the alarming sight of my face reflected on the screen — scrunched up, red, demonic-looking.
(I still haven't recovered from the alarming sight of her neck cords bulging as she gets pleasurably whomped on the rear by Michael Fassbender's Carl Jung, in "A Dangerous Method").
The hollow ring of empty rhetoric The most alarming sight at this year's Labour Party conference was the spectacle of platoons of pinkish hacks believing Tony Blair.
