It won't work how you hope.
The reason is that the Knock app has to be actively running in the background (such as if a screensaver/lock screen activates, all programs continue to run in the background).
If you're at a log in screen, meaning you aren't already logged in (which means Knock isn't running in the background), you can't unlock it with your phone.
Kind of a big limitation I did not know until after the fact.
Many lock screen shortcuts use the fast user switch login screen, and it would not work for this because it means the user is logged off and nothing is running in the background.
So, there are two instances where I found Knock works (also confirmed by their FAQ):
When the screensaver activates and you need a pw to unlock.
When selecting "lock screen" specifically from the Knock icon in the system tray.
All other instances seem to cause Knock to stop working in the background. If it's not running then it's not synced, so it won't unlock.
I guess all this extra info answers your question that no, you won't be able to use this to initially log into a profile, or to quickly switch profiles between you and your wife.
However, if you already logged in manually into your profile with your keyboard the first time, and happen to step away (activating the screen saver lock screen), it will work fine for yourself to re-unlock as many times as you need to, until you log off. You'll just have to initially log in manually that first time every time.
(BTW, sweet Apple setup in your sig. It's time to replace that iPad 3rd gen with an Air! (I just ordered mine to replace my 3rd gen). I almost didn't, but I realized it is laggy, and I understand why it was replaced 6 months later with the iPad 4. If I had an iPad 4, I would probably hold onto it. With the iPad 3, too much of the resources are going just to power that retina screen. Anyway, random rant of me trying to justify my purchase, lol...
)
