The new "OK, Google" hotword detection will let you start a Google Now search from any screen on your device, even the lockscreen. This change rolled out last week, but despite a couple of updates to the app from the Google Play store, many people are still reporting that they aren't seeing this set of options in the Google Now app.
When you spontaneously remember something you need to do at a future time or date while using your device, you can simply say, "OK, Google," and then the Google Now interface will be at your service. Ready to add this option? Thanks to Reddit user pr01etar1at and the site AndroidPolice, here's how:
Note: This feature may be limited to Android 4.3 and up for now.
Edit: Some users are reporting that this only works on their Android 4.4 and up devices, so you may need to update your Android version before you can use this functionality.
Update: Make sure you're on the latest version of Google Search from the Google Play Store before attempting to enable this feature. (Thanks, netjeff!)
Update No. 2: Canadian users can switch the input language to English - US to enable this feature. (Thanks to Twitter user @_gwh_.)
Tap the menu button on your device and choose Settings > Voice > "Ok Google" Detection.
Check the box next to "From any screen" (and also "From lock screen" if you choose).
You'll have to agree to the terms provided by Google, and then teach the app what your voice sounds like by saying, "OK, Google" three times.
That's it! Now you can use Google Now when using another app, or just after waking up your device.