Is the route of concealed gas pipelines detectable?

In an old apartment building, renovated several times at some point in the past, gas pipes are installed under the plaster or in ducts.

Is it possible to reliably determine their course somehow?

There are water pipe and electrical cable detectors.

Do they also work reliably for gas pipes?

Tobias

The detectors for power cables that I know work reliably with metal. What are the gas pipes made of?