Context: I work on web development for a small company. We are two on the department and the other guy is on holidays. Another one on the company asked me to basically be on reach for the full 8 hours of a full-time turn (I'm part-time, I work 4 hours), and connect my computer to the one that's on the office to be able to solve emergencies. All of this, unpaid, since I'd still get only the 4 hours salary.
I'm based in Spain so I'm sorry if there are errors.