Bellow
Bellows are able to sense small pressure differences. Bellows can be sealed in a container (Figure A) or exposed to the external environment (Figure B). Bellows range in size from very small to very large. Bellows have a very distinct shape as seen in the figures below. Lastly, a bellow can be made from any material, from plastic to lead.
Aneroid barometers utilize a bellow to measure the change in air pressure in a particular place. Understanding air pressure changes can helped to forecast weather. Meterologists utilize barometers and other indicators (i.e. the wind, temperature, moisture, and cloud formations) to provide you with a forecast (Bureau of Meteorology, n.d.).