What does “a canary in the coal mine” mean?

It is a bird that has been used by miners.

Which of these sentences is using “a canary in the coal mine” correctly?

The broken coffee machine is a canary in the coal mine for our office.

Her promotion is a canary in the coal mine for the company’s success.

The spilled coffee is a canary in the coal mine for my bad day

The decline of bee population is seen as a canary in the coal mine for broader environmental.

A canary is the coal mine refers to an early warning system.

The sudden drop in sales could be a canary in the coal mine for the company’s overall financial health.

She’s a canary in the coal mine of our team

The new policy is a canary in the coal mine.

The backlash against the new policy could be a canary in the coal mine for future public opinion.

The delay in the meeting schedule is a canary in the coal mine for the project’s failure.