StrideX is the watch companion of an open-source, do-it-yourself foot sensor. It does NOT work on its own: you need a StrideX sensor (Seeed XIAO nRF52840 Sense) in watch mode on your shoe. Build instructions, firmware and code are on GitHub (see project StrideX). What it does Connects by Bluetooth to one or two sensors (left and right foot). Starts and stops the sensor recording with your run. Shows live metrics computed on the shoe: effort score (% of your MAS), pace, cadence, slope and average speed, together with your heart rate. Records a normal activity (GPS track, heart rate) and adds StrideX fields to the FIT file. The sensor keeps the stride data, which you analyse afterwards in the StrideX phone app.