Bourdon tube or Diaphragm type mechanical dial gauges do not require external power source.
Bourdon tube pressure gauge consists of a hollow tube which curves within itself. The end at the extremity of the curve is closed off, whilst the other end is open and therefore free to experience pressure exerted upon it, in this case from fluid flowing through a pipeline. As pressure increases, the tube unfurls a little, pushing its capped end outwards. This movement is picked up by a link bar and directed into a pivoting arm, which is geared to magnify movements in the measurement needle. That’s it. The Bourdon tube gauge is a simple yet effective mechanically operated instrument, one which is widely used (similar technology inside many barometers, where it is employed to detect changes in atmospheric pressure.)
The diaphragm gauge uses as a pressure-responsive element, a thin, circular, (usually) metallic plate, either flat or corrugated to avoid buckling.
The mechanical pressure gauges are usually damped to avoid damage due to sudden variations in the air pressure being measured. Hence for the purpose of precise data collection for monitoring purposes, electronic pressure sensors are suitable to detect the variation at a sample rate of 1 second.