Modern technology has evolved to include various health and fitness trackers to help people become more aware of their physical wellbeing. However, the reliability of these technologies is not well-established. The purpose of this research was to determine the reliability of Stryd accelerometer during trail running. Participants wore one Stryd accelerometer (model 25; Stryd, Boulder, CO 80301) on the laces on each shoe (left and right), and the devices were started simultaneously. Each participant then did a self-paced out and back run on a moderate difficulty hiking trail. The trail began at approximately 6000 feet elevation and climbed approximately 200 feet/mile. After ten minutes of running up the trail, the participant turned around and returned on the same trail. After the run, the Stryde accelerometers were stopped simultaneously. The Stryd data (distance, altitude, speed, power, form power, cadence, vertical oscillation, and leg stiffness) was exported to csv files and divided into the uphill and downhill phases of the run based on the peak elevation achieved. The within-subjects coefficient of variation and the mean absolute difference for each measure during downhill and uphill trail running was calculated. Of the mentioned variables, six were considered reliable - CV 0.1. The least reliable measures were form power (uphill: CV=0.124; downhill: CV=0.126) and power (uphill: CV=0.132; downhill: CV=0.135). As most of the measured variables were statistically similar, the Stryd accelerometer can be considered reliable. However, with three sensors that were statistically unreliable, it is important for the user to know that the Stryd's advertised ability to measure power output is less reliable on inclines and declines and may provide inaccurate training advice. These findings give reason for further development of the technology.