on duty

Idioms  

1. At one's post, at work, as in The new nurse was on duty that evening, or The watchman was fired because he was drunk on duty. [Mid-1600s] The antonym, off duty, means “not engaged in one's work,” as in Captain Smith was much more amiable when he was off duty. [Mid-1800s]

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Example Sentences

The ruling that Bondi appeared to reference involves a separate California law requiring law enforcement officers to display identification while on duty.

From Los Angeles Times

Bass later removed Crowley, citing the failure to keep firefighters on duty for a second shift.

From Los Angeles Times

It would have been up to the custody sergeant on duty to verify the suspect's identity - which, in the circumstances, will not have taken long.

From BBC

But as the deaths continued, the neonatal consultants had noticed she was the one person who seemed to be on duty.

From BBC

Recent US media reports have said ICE officials were expected to be on duty at Sunday's showpiece at Levi's Stadium in Santa Clara, the home of the San Francisco 49ers.

From Barron's