The invention relates to a pipe system comprising a pipe, a gas sensing station and a remote output system. The pipe comprises a pipe gas cavity, such as an annulus, extending lengthwise in part or all of the length of the pipe; the gas sensing station comprises a sensing gas cavity which is in gas communication with the pipe gas cavity: The sensing gas cavity comprises a photoacoustic spectroscope. The pipe system comprises at least one optical feeding fiber for feeding light to the photoacoustic spectroscope and a transmission path for transferring a signal from the photoacoustic spectroscope to the remote output system, the transmission path from the gas sensing station to the remote output system is an optical transmission path.The pipe may for example be a flexible pipe e.g. an umbilical or a pipe for the transportation of crude oil from a well to an off shore or on shore station, for example a ship or a platform.The gas sensing station may be integrated in the pipe, e.g. in an end fitting or it may be an external gas sensing station.According to a high security embodiment of the invention it is desired that all energy transported between the remote output system and the gas sensing station is in the form of optical energy e.g. transported in one or more optical fibers. This embodiment provides a very safe and simultaneously well functioning system, with reduced risk of igniting burnable fluids and simultaneously with a high signal-to-noise quality.