This shows swaylock being used with the keyboard addon. First I turn the screen on and provide my password. As you can see for a bit in the top left corner, Sxmo was in the locked state prior to unlocking with the password. Then I turn the screen off again and let the device suspend. I wake it up with another power button press and am again greeted by a password prompt. This time I do not provide it and it goes back to suspend after 8 seconds of inactivity.

Instructions on how to get this working for your device can be found here: https://lilyb.it/tech/sxmo#lockscreen

Apparently touchscreen-based forks of swaylock that add a numeric keypad also exist, they are linked in that blog post as well.