Like the Moto X, the Nexus 5 also has a dedicated low power audio processor for always-on “Ok, Google Now” functionality. However, the feature is only partially implemented and works only on the home screen. Many users had hoped that third party apps or custom kernels would enable this feature even when the device is sleeping but the closed source nature of the dedicated audio processor acted as a big roadblock.

https://youtu.be/F1ANpeexBTQ

Now, a member of the OmniROM team — Guillaume Lesniak — has posted a video that shows off Always-on “Ok Snapdragon” voice recognition feature in action on the Nexus 5. The developer has managed to use the dedicated low-power audio core on the Snapdragon 800 chip for this purpose which means that there will not be any hit on battery life as well. 

The functionality, however, is only a proof of concept and requires heavy modifications to the audio HAL and system libraries to work properly. While the developer might be able to polish the feature enough to bake it into custom ROMs, the chances look bleak because of Qualcomm’s re-distribution licensing issues.