How does the screen-off-gesture-detection work

[toches]

I'm wondering how the feature in the OPPO that recognize screen gestures, while the screen of the device is off, actually works? For example, the feature to double tap to awake the phone, or draw a circle to open the camera app. Does the screen really been turned off, or actually the screen is on, and just the screen is black. (this way the screen is on, hence can recognize the gestures, and on the other hand save battery energy).

I would also like to know from those of you that already has the OPPO, are those screen-off-gestures are battery friendly? Can you notice difference when turning off this feature?

 

[TheTrueSpin]

The screen is actually two components. One part displays the visual information you see and the other senses touch. All that's happening is that the latter is left on so that touches can still be registered. The LCD is indeed off.

 

[toches]

The screen is actually two components. One part displays the visual information you see and the other senses touch. All that's happening is that the latter is left on so that touches can still be registered. The LCD is indeed off.

Thanks for the answer! Can you please refer me to some report or a tech blog dealing with this issue?
I also looked at the specs (http://www.gsmarena.com/oneplus_one-6327.php) of the OPO, and found nothing indicating this feature, how does OnePlus call it?

Last question, are there more smartphones that has this feature? I found an app called Knockr (https://play.google.com/store/apps/details?id=tecnology.angs.knockr&hl=en) that does something similar to the OPO feature and targeted to Galaxy s5 and Moto X.