This study examined the criterion-related validity and the reliability of the FitSense FS-1 Speedometer for estimating distance, speed, and energy expenditure (EE) during walking and running. The study was divided into two parts. Part I investigated the validity and the reliability of the FitSense for estimating distance while walking and running around a 400-m track (n = 24). Part II looked at the validity of the FitSense for estimating speed and EE during level treadmill walking (4.8, 6.4, and 8.0 km · h-1) and running (8.0, 9.6, and 11.2 km · h-1). Twelve of the original 24 subjects completed Part II. The results of Part I indicated that the FitSense accurately estimated walking distance, but it underestimated running distance by an average of 3.5 % (p = 0.016). Test-retest reliability was deemed adequate for both walking and running distance (ICC = 0.87 and 0.84, respectively). In Part II, the FitSense overestimated speed during treadmill walking at 8.0 km · h-1 (p < 0.001) and underestimated EE at two walking speeds (6.4 and 8.0 km · h-1) (p < 0.01). No significant differences were found for speed or EE predictions while running at any speed. In summary, the FitSense FS-1 Speedometer provided valid estimates of walking distance during track tests, and valid estimates of speed during treadmill walking (4.8 and 6.4 km · h-1) and running (9.6 and 11.2 km · h-1). However, the FitSense underestimated running distance during track tests. In addition, the FitSense overestimated speed and underestimated EE in the transition between walking and running (8.0 km · h-1).