Cyanogen team is working on several innovations such as Smart Call, Smart Dialer, True Silent mode, etc. to make its Android 5.1 based operating system CyanogenMod 12.1 more usable and feature rich. However, not all features are currently available in the CyanogenMod 12.1 Nightly build. At present only “Smart Call” feature is available.
CyanogenMod 12.1 Nightly brings Smart Call function to your phone. The “Smart Call” feature makes it easy to call your contact. All you need to simply move your device to your ear to place a call. You can also answer a call by just placing the phone to your ear, but currently only Smart Call functionality is available on CyanogenMod 12.1 Nightly build.
CyanogenMod has also restored the missing True Silent mode in CyanogenMod 12.1, but at the same time, it will not mute alarm. However, the so-called “zen mode” will shut down everything – alarm, notification, LED notification, etc.
CyanogenMod 12.1 Nightly build is now available for many devices. You can download the CyanogenMod 12.1 Nightly build for your device from this link [HERE]. Install it and taste the new features. (Source)