What device in gas service is designed to automatically shut off fuel supply?

The device designed to automatically shut off the fuel supply in gas service is the safety shut-off valve. This valve plays a crucial role in ensuring safety by preventing gas leaks in situations where there is a failure or abnormal condition, such as an excessive flow of gas or a system malfunction. When the safety controls detect an unsafe condition, the safety shut-off valve closes, stopping the flow of gas to prevent potential hazards like explosions or fires.

While pressure regulators and electronic valves may control gas flow or pressure, they do not have the primary function of shutting off the gas supply in emergency situations. A flow meter is primarily used to measure the quantity of gas flowing through a system, but it does not shut off the fuel supply. Thus, the safety shut-off valve is specifically engineered for the critical task of cutting off gas flow when safety is compromised, making it the correct answer.