A variety of methods have been used to analyze the kinetics of various processes related to the Diet Coke and Mentos experiment (also known as the soda geyser). However, none of these previous reports has undertaken a quantitative exploration of the dynamics of the creation and collapse of the soda geyser itself. We have therefore devised a method for monitoring the time dynamics of the height of the fountain generated when Mentos candies are added to Diet Coke. The procedure involves collecting a video of the fountain using a smartphone and subsequently analyzing the video using a smartphone application. It is noteworthy that the protocol can be used to investigate a process that lasts only 3-4 s with a time resolution of tens of milliseconds.