In this paper a wearable electronic-free micro-fluidic device for the continuous monitoring of pH in sweat during exercise is described. The sensing capability is based on ionogels, ionic liquid hydrogels, containing pH sensitive dyes capable of reporting pH activity in the range from 3 to 10. Previously, we reported a flexible micro-fluidic barcode capable of measuring the pH of sweat in real time . Here we have improved the device in terms of wearability, physical robustness, chemistry of the sensor and its optical response by using a mobile phone for data collection and a more accurate algorithm for colorimetric image analysis. Copyright © (2011) by the Chemical and Biological Microsystems Society.