Most of what Google has done in lollipop is great—better design, thoughtful features, and better developer support. However, there are few wonky things going on in this first release, and it's hard to know if they're intentional or not. Case in point, the lack of silent mode on phones. Lowering the volume only offers vibrate mode, and the new priority notification system isn't going to help you.
So here's the deal in KitKat—you lower the volume and it goes to vibrate. Lower again and it's completely silent. Cool. In Lollipop on phones, you lower the volume to zero and it kicks over to vibrate, and that's all you get. Hit up and it goes to volume 1, down and it's still just vibrate.
There's no setting that prevents all your notifications from getting through unless you use the new "None" notification mode. This comes with one inexcusable drawback, though. "None" doesn't allow alarms to work, which is just bananas. I can't think of a scenario where I wouldn't want alarms I had previously set to be audible. To make matters worse, you can change these modes from the lock screen without entering the code. So if you want to really troll your friends/enemies, you can set their locked phones to "None" and their alarms won't go off. Check out Motorola's video below for a demo of how this all works.
Perhaps even more odd than the omission of silent mode on phones is that it's still available on tablets, more or less. On a Lollipop tablet like the N9, simply lower the volume to zero and let it go to vibrate mode. Then hit the volume up toggle and you get 0 volume (alarms will still work normally). The inconsistency between form factors is baffling. I guess we'll see if this is a bug or not when Google starts the next round of updates.
On a tablet you can set volume to 0
Update: With further testing, we've found that you can get 0 volume on a phone by rebooting when you've hit volume up and set it to level 1. The device comes back up with silent mode engaged like a tablet. However, you have to reboot every time. One of these two situations is a bug, but it's hard to know which one.
Update 2: There's a thread in the issue tracker now if you want to offer additional information to help get the problem fixed.
[Reddit – Thanks, Steve Kilburn]