Update is designed to monitor and transmit pressure and temperature data of an underwater pipeline during the hold period of a hydrotest, while the accompanying marine-support vessel (MSV) is free to travel upwards of 9.5km from the testing site. The system, which comprises both underwater and surface components, measures and stores data which is transmitted through water to the surface assembly on an MSV. It also incorporates a fail-safe memory card from which information may be downloaded, even if battery life has expired. Typically, the hydrotesting procedure calls for the use of divers and an MSV which must remain stationary for the standard 24-hr pressure-hold phase while data is transmitted from the pipeline through a line to the surface assembly onboard. As a result, the cost of a traditional hydrotest is substantially greater because it ties up the use of an expensive marine vessel. The system was rigorously tested throughout 2001, and already has firm commitments to be used extensively on behalf of clients throughout the 2002 season. It is designed to operate in extreme environmental conditions and difficult acoustical terrain such as that found in the North Sea.