the coast [is] clear

used to say that everything is safe and someone can proceed to do something

The idiom "the coast is clear" likely originated from nautical terminology, where it referred to a situation where the sea and coastline were free from obstacles or dangers, allowing for safe passage. In its modern usage, it refers to a particular situation that is now safe or free from any potential threat, allowing someone to proceed without fear of being discovered, interrupted, or facing an obstacle.

He peeked around the corner to make sure the coast was clear before sneaking into the forbidden room.
Before leaving their hiding place, the fugitives waited until nightfall and confirmed the coast was clear.
He peeked around the corner to make sure the coast is clear before sneaking into the forbidden room.
After a thorough security check, the guards determine that the coast is clear for the VIP's arrival.
The burglars waited until the alarm system was disarmed and the street deserted, making sure the coast was clear before attempting a break-in.