The phrase "alarming sight" is correct and usable in written English.
It can be used to describe something that causes concern or fear when observed.
Example: "The abandoned building was an alarming sight, with broken windows and overgrown weeds surrounding it."
Alternatives: "disturbing view" or "frightening 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.
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.
Some time later, Polybius goes on, the Romans themselves encountered the terrifying trumpets and horns of the Celts, which — along with the alarming sight of the tall, blond naked warriors — helped lead to the Roman defeat.
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.
Even in an industry that lionises freaks - Karl Lagerfeld, John Galliano, Anna Piaggi, Isabella Blow, Gareth Pugh and so on - Rick Owens and his wife Michele Lamy have to rank as one of fashion's most alarming sights.
Jobless men were already roaming the roads, an alarming new sight for townspeople not used to such things.
What is surprising and alarming is the sight of them using excessive force against protesters.
Late last month, villagers in Guinea's remote south-eastern region of Nzérékoré were greeted by a sight so alarming that many barricaded themselves indoors.
So when a DC-9 belonging to Aeropostal, a state-owned Venezuelan airline, lost both of them upon landing last week in Puerto Ordaz, the sight was alarming, even though fortunately the injuries to passengers were slight.
