cop

[keitra]

What does the following sentence mean? When police officers are sick at home, they have to call for permission to leave the house, and check in again when they return.

[Ewood27]

Seems clear enough to me, keitra. Assume you are a police officer. You are ill. You telephone your police station and say you are ill and cannot come in to work. To make sure you're not cheating and claiming to be sick so that you can do something else rather than work, they will expect to be able to telephone you at home at any time and find you there.
If you need to leave the house, say to go to your doctor's, you must first telephone the police station and ask permission. Then when you return you must telephone again and tell them. It's to help guard against officers who might, perhaps, "go sick" every Saturday afternoon in winter so that they can play football.