Double tap to wake up

You can try a custom rom or some apps in the Play Store, but as far as I know they are going to use a lot of battery juice. It doesn't work very well if that feature wasn't built in your phone.

It's very easy to lock your screen though using some apps (screen off & lock is my choice), and you can even set a gesture for that action when using a third party launcher, as Nova.
 
I don't think it will make it to the Moto G (2015). As stated above, you'll likely need to use a ROM or custom kernel to have this feature if it's supported.
 

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