Originally Posted by khaytsus
That's because it wasn't supported at a low level like it is on the G2. Other devices it requires a wakelock or partial wakelock.
As for the OP, no, knock-on uses immeasurable battery. Some people say that I believe "Android System" usage drops if you disable Knock On but I have yet to see anyone show any real information that it changed battery life.
I'm not a heavy user but I take my phone off charge at 7am and put it back on at 11pm and it's at 80% or so most days. I could easily go two days, but I'd prefer the more shallow charge cycles to make the battery last as long as possible.
In my specific case, disabling Knock ON/OFF has improved battery life significantly, dramatically, from 49% drop (from 100 to 51) over 8-hour night (doing nothing) to 2% drop over the same period of time, again, doing nothing.
Official CM10.1 Nightly @ 1000MHz NOOKcolor
Offiical CM11 KK Nightly on Kindle Fire 1st-Gen
Rooted Kindle Fire HD 8.9" w/ Nova Launcher
Virgin JB 4.3 on Sony Xperia Tablet Z
Rooted stock-ROM KK 4.4.2 on LG-D800
Virgin Samsung Galaxy Tab 2 10.1 - LOST
Slimbean 8.1 on Galaxy S2 i777 - LOST