noun, noun which may take the genitive case particle 'no'
Refers to a loud warning device, such as on emergency vehicles or in air-raid alerts. Also used attributively with の.
救急車のサイレンが聞こえた。
I heard the ambulance siren.
サイレンの音で目が覚めた。
I woke up to the sound of a siren.
Borrowed from English 'siren'.