Saying "OK Google" or "OK Moto X" are typical ways to launch the Moto X's personal assistant, the Moto Voice. But on the 2nd generation of the Moto X you get to use a custom launch phrase to call the Moto Voice.
To launch Moto Voice on Moto X using a custom sound or voice (phrase launch), do as follows:
1. Open the Moto application on the Moto X (2nd gen) and tap the Gear icon to open the settings
2. Tap the Voice option and then head to the Manage Launch Phrase settings
3. Now tap the Change or improve Launch Phrase option
4. Make sure to select the "Choose something you'll remember" option, instead of the "OK Google Now" option
5. Tap the Next button on the bottom, read the instruction and record your new custom launch phrase.
6. Once you are done setting up the Moto Voice launch phrase, you can easily use that specific phrase to enjoy your Moto X more
** A fun tip: Use a whistle as the launch phrase