If only Siri can be activated the way Google is activated on Android by just saying "OK Google". The only way Siri even comes close is the "hey Siri" option.
It's not activated on every android device - only ones with a special chip - my question is - what is the battery life on that device (I believe only one nexus phone has it - correct me if I'm wrong). Android is notoriously bad on battery life - I doubt this feature helps it.