greenmanSit up and take notice

This idiom is very common and means "to start paying attention or show an interest in something".

E.g.

No one took them seriously until they won the election; then everyone sat up and took notice—Nadie los tomaba en serio hasta que ganaron las elecciones; entonces todo el mundo empezó a prestarles atención

The terrorist attacks in Paris made Europe sit up and take notice—Los atentados de Paris hicieron que Europa reaccionara y tomara nota