Guys from JDB Pocketware (creators of legendary PocketShield) have risen up a concern and written an open letter to Nokia regarding what could be a potential battery drain issue on the Nokia Lumia 920:

Nature of Windows Phone buttons

Pressing either the power button or the camera button will cause the device screen to turn on, even when the proximity sensor detects proximity.

The lockscreen behavior
Upon power on, screen lights up and shows the lockscreen (or camera), which runs a timeout to auto power off the device if screen is not touched in X seconds.

But if screen is touched, the timeout counter is restarted, so continuous touching could lead into a loop, the “death loop” which won’t let the device to power off (standby) and will consume battery power.

New touchscreen technology
The Nokia Lumia 920 comes with a touchscreen that reacts to touch from pretty much any material such as metal or clothes. This can be dangerous…

So here is a theory
When the phone is inside a pocket or bag it can be touched by other objects. These objects can press buttons and can touch/rub the screen. This will initiate the “death loop” for who knows how much time, could be minutes or hours, depends on how active the user is since body movement will produce friction between objects/clothes and touchscreen.

The “death loop” will drain battery and battery is precious.

Solution?

Should be simple: screen must not power on if the proximity sensor detects proximity. Current version of Windows Phone does not take care of this. The big question is: will Windows Phone 8 take care of this? Is the Lumia 920 a potential battery drainer?

Source: JDB Pocketware blog