The purpose of this article is to explore how sensors work in a smartphone with respect to activity recognition and more specifically, how a pressure sensor can improve the results if integrated with an accelerometer. In order to show that, a set of experiments were performed on a user who uses the Samsung SIII. The user was asked to perform a set of daily activities such as standing up, jogging, walking up and down the stairs. The results show that a detection of a change in the pressure that is being subjected to the smartphone would give an indication of the user's altitude and activity. This indication helped in improving the activity recognition when it is combined with the data obtained from the accelerometer.