One must take steps to activate this (9)
I believe the answer is:
pedometer
'one must take steps to activate this' is the definition.
(a pedometer measures steps when walking)
This is the entire clue.
(Other definitions for pedometer that I've seen before include "Walker's distance measurer" , "Walkers' measuring device" , "counter for walkers" , "Measure of progress" , "It records steps taken" .)