Some android devices (Nexus 7 included) have a magnetic sensor under the screen, located so that a magnet in the cover being removed by opening the cover wakes the device up without needing a swipe. For the N7, there is a magnet hack mod for a Kindle Fire cover to make it work on when used on the N7 (described in the XDA forums).
Does a kindle fire have that mag sensor?
Aww... found the video. No button press needed, but still need swipe:
There may be a software hack to detect the magnet and bypass the swipe.