What function does the "service button" in an elevator serve?

The function of the "service button" in an elevator is to allow for specific control of the elevator during maintenance. This feature is essential for technicians and maintenance personnel as it provides them with the ability to run the elevator in a controlled manner, enabling them to perform checks and repairs safely. When the service button is activated, it often bypasses certain safety protocols and allows for functions that are typically restricted during normal operation, thereby facilitating maintenance tasks without the risk of interference from passengers or other external factors.

The other options represent functions that are not associated with the service button. For instance, opening all doors simultaneously is not a practical feature of the service button since it could endanger passengers. Increasing the speed of the elevator would compromise safety, as elevators are designed to operate within specific speed limits for the safety of users. Lastly, turning on emergency lights is typically managed through a different mechanism designed specifically for emergency situations, and not through the service button.