Lock screen of Nexus 5 during active call How can I activate my PIN lock screen by default during an active call? If my proximity sensor turns the screen on during the call I frequently drop will accidentally disconnect by clicking the "end" key inadvertently. 

Nexus 5, 4.4.3, Stock Android/Nexus 5
Go into Settings -> Accessibility -> Uncheck the checbox power button ends call. Now during call, when you press the power button, the screen locks; Pin/Pattern/Password screen appears.

I have tested on my device but not on nexus 5. Have to do in emulator.