Activated when attacked (6,2)
I believe the answer is:
turned on
'attacked' is the definition.
(to turn on someone is to betray or attack them)
'activated when' is the wordplay.
'activated' becomes 'turned' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'when' becomes 'on' (I've seen this in other clues).
'turned'+'on'='TURNED-ON'
Can you help me to learn more?
(Other definitions for turned on that I've seen before include "Stimulated" , "Feeling great excitement" , "Excited" , "Suddenly attacked - state of ecstasy - high" , "TV working?" .)