Nope it didn't but its been introduced with lollipop to devices that support it, I believe the nexus 6 supports it. I meant I wish we could wake up the device saying "OK Google"... No we never had it. Moto x does as a feature based on its design.
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I was expecting that this feature arrives on the Nexus 5, but I have a number of possible reasons why it didn't arrive.
First of all the Moto X 2013 and 2014 both have a special low power voice detection chip, if you check the specifications page:
This special kind of chip is limited to high end Motorola devices and I hear that it is on the Nexus 6 as well, maybe that's why it has voice control when screen is off.
However! The Nexus 9 also has this feature and it's an HTC device and all Snapdragon 800(and above) devices have their own DSP for low power voice detection(albeit not as good as Motorola's chip).
Maybe they decided not to give it to the Nexus 5 because it would cause battery drain and the Nexus 5 doesn't have the best battery life as is.
I personally might be moving to a Custom ROM soon if it offers voice control when phone is off, *cough* ParanoidAndroid maybe *cough*.