In this activity, learners use simple items to construct a device for indicating air pressure changes. Learners build water barometers (also known as "storm glass" barometers) and record the height of the water in the device for 10 days. Learners observe how the changes in water level relate to the changes they notice in the weather. This lesson guide includes background information about air pressure, the history of barometers, and how pressure relates to weather and thunderstorm safety. Learners can also build a "dry" barometer by following the instructions in the related resource.