What device is used to measure atmospheric pressure?

A barometer is the device used to measure atmospheric pressure.

Atmospheric pressure is the force exerted by the weight of air above a location. A barometer detects this pressure and commonly displays it in hectopascals, millibars, or inches of mercury. Falling pressure often signals unsettled weather, while rising pressure is commonly associated with improving conditions, though weather forecasting uses many measurements together.

The first major barometer was developed by Evangelista Torricelli in the 17th century. His mercury barometer used a glass tube filled with mercury and inverted into a reservoir. Air pressure pushed on the reservoir, supporting a column of mercury whose height changed as pressure changed. Modern instruments often use aneroid barometers, which measure pressure with a sealed flexible metal chamber instead of liquid mercury.

An anemometer measures wind speed, a hygrometer measures humidity, and a thermometer measures temperature. A pressure altimeter uses the same basic pressure relationship to estimate altitude, but a barometer is primarily used to monitor pressure at a location.