Jan Peter van Zandwijk
Abdul Boztas

Abstract

The iPhone Health App automatically collects data on daily activities for health purposes. Detailed information on the number of steps taken and distances travelled is stored in a database together with timestamps with a time granularity of a couple of minutes. While such information can potentially be very valuable in a forensic investigation, one needs to have a good understanding of its reliability in order to make proper use of it.

In this study we investigate the accuracy of steps and distances registered by the Health App under a broad range of experimental conditions for an iPhone 6, iPhone 7 and iPhone 8. For five subjects, we varied carrying location of the telephone, walking distances, walking speed and compared steps and distances registered by the telephone to manually measured steps and the real distance.

The results of the experiments were similar for all three telephones. Steps registered by the iPhone Health App agree very closely to those measured manually with an averaged error of about 2%. The reliability of the registered distances, however, depends on a number of factors, including walking speed and walking style of the subject and can deviate up to 30-40% from the true value.

These results suggest that, if you take the properties of the iPhone Health App into account, digital traces from the Health App can be used for evidential purposes, for example to make a probability statement about different routes that may have been travelled in a case.