How do I keep my camera active on Android even when the phone is locked and screen sleeps? When I play Ingress, Ingress remains active. Even when my screen goes black, if I push the power button, Ingress is still active. I do not need to unlock my phone nor wait for it to "wake up". (The phone is locked though - to use any other app I need to unlock the phone.)

How do I get the same functionality for my camera app?

If I'm using the phone as a camera, with the camera app active, if the screen goes black, when I hit the power button, I want the camera to be open and active.

Things I've tried: 


Keeping my phone unlocked when in paired to a trusted Bluetooth advice. Then when I push the power button, I get a screen where I have to swipe to wake it up. With Ingress, I don't have to swipe the screen nor wait for anything. 
Snapshot. I've tried using the Snapshot app, but I have to wait for the phone to launch the camera app. 
The camera on swipe from the lock screen ... and again I have to wait for the camera app to launch.


I'm willing to figure out how to build my own app if needed. (But would rather find something.) 

I'm willing to take a battery hit.
Well it depends on your android version however supposing you are using lollipop you can lock up an application to only make that one work. And you can download an app called caffeine from play store that avoids your phone to go stand by. If you don't want to be notice by any means, you can download an app called spy camera HD pro by MVM studio.