Validity of FitBit, Jawbone UP, Nike+ and other wearable devices for level and stair walking

•Step count errors were less than 1% for most monitors for over ground walking.•Stair walking caused step count underestimation and distance overestimation.•All devices overestimated distance by at least 45% for stair walking.•Nike+ FuelBand was the least accurate activity monitor for all walking tasks.