A huge proportion of the world population is suffering from lifestyle related and preventable welfare diseases. Physical activity is one important means of achieving beneficial health impacts and of reducing the risk of chronic disease. Pedometers are often used to measure physical activity. Nowadays, cell phones are very common, and pedometer applications enable measurements to be made by a device that is already owned. This chapter presents a study of the measurement accuracy of pedometer cell phone applications. The results show that only one combination of pedometer application and cell phone provided high accuracy when tested by different test persons. In some cases, the measurements indicate that the orientation of the cell phone used during measurement might be relevant. In addition, it would be valuable to gain knowledge about the overall and everyday physical activity pattern, which would be very valuable in contributing to a healthier population.