For those unfamiliar, Silent Mode is when users lower the volume all the way down where it will first enter into Vibrate mode. Press the volume button down again and it will enter Silent mode which basically means there will be no audible alerts and no vibrations either. Oddly enough in Android 5.0 Lollipop, it has been noted that Silent Mode does not exist at all.
Now we can’t be sure if this is a bug or if it is a feature that has been removed entirely by Google, but many are perplexed by it. The only way to disable both audible alerts and vibrations is by choosing the “None” notifications mode, which in turn will also disable any alerts you get from alarms which is definitely not a very good alternative.
Silent Mode, however, can still be found on Android tablets like the Nexus 9 so it seems odd that Google would remove that feature for phones and not tablets, thus leading us to think that maybe it’s a bug. Now there is a workaround which is that you will have to lower your phone’s volume down to 1, reboot the phone, and you should be in Silent Mode, although this does seem like a very convoluted solution, but one that Google will hopefully address soon.