Android 6.0.1 Marshmallow introduced a new shortcut wherein double-tapping the power button twice would open the camera app. However, this feature has its own caveat wherein if the phone or tablet is unlocked and the power button is double-tapped, the device will forcibly lock the device before launching the camera app.
This limitation has persisted through all versions starting Android 6.0.1 through Android N Developer Preview 2 (DP2). Google has now introduced a fix in Android N Developer Preview 3 (DP3) which enables quick access to the camera app by double-tapping the power button and without locking the device.
Here is how the 'double-tap to open camera' feature works in Android N DP3 (courtesy Android Police):
- If device is unlocked, double tap opens the camera and device stays unlocked
- On lockscreen with smart lock enabled (swipe to unlock): double tap opens the camera and unlocks the device
- On lockscreen with device locked: double tap opens the camera, but device stays locked
- Without lockscreen functionality: double tap opens the camera