Google prepping a fix for the Double-tap to wake bug on the Pixel and Pixel XL?
You can enable Double-tap to wake on the phone
But now, there apparently is a new issue with the first smartphones designed by Google (and built by HTC). The Double-tap to wake feature, which was added to the phones with Android 7.1.1, is apparently not working consistently on some units. A few reports say that the Double-tapping fails to work when power saving feature Doze is on. With Doze, the phone disconnects apps from running in the background after a period of inactivity. This increases standby time and battery life. To turn off Doze, all you have to do is move the phone around. One workaround that might help is to change the Pixel's lock feature to read "immediately" after sleep.
Some Pixel owners have been sounding off about the problem in the Pixel User Community. The Double-tapping feature is used to wake up the phone and also allows users to see their notifications. For what it's worth, Google is aware of the issue too, and is working on a fix. Stay tuned!
source: GoogleProductForums via 9to5Google