What device is used to measure the volume of natural gas used in a building?

A gas meter is specifically designed to measure the volume of natural gas that is consumed by a building. It works by registering the flow of gas passing through it, allowing utility companies to bill customers based on their actual usage. Gas meters are essential for accurately tracking consumption, ensuring proper billing, and monitoring usage for safety and efficiency.

In the context of the other options, while a pressure regulator helps to maintain the pressure of the gas within the proper limits for safe operation and a flow meter measures the rate of gas flow, a true gas meter is distinct in that it specifically quantifies the total volume of gas used over time, making it the correct choice for this question. A septic tank monitor, on the other hand, is unrelated to gas usage measurement and instead relates to wastewater management.