Two ways. Natural gas is odorized and is meant to be sensed as a smell, so it is often obvious. Or, P.G. & E will notify customers if they suspect a leak. Any leak found on the house side of the meter is the property owner’s responsibility to remedy.
Flexible gas piping can save time and money when replacing an existing system. Its much easier to service those “hard to reach” places under existing homes with a flexible pipe. When room and space is sufficient, however, steel can be the best choice as it is less expensive.