Here’s the same question, but I don’t think it’s well answered because the phone will keep registering touches when in-pocket:
Method of typing input while the screen is off
I’d like to be able to take out a small Bluetooth keyboard and immediately start typing some notes into it like an Alphasmart but without seeing what I’m typing. How can I do that?
The first issue, as far as I can tell, is the screenlock.
The second issue might be delay as the keyboard wakes the phone and switching to a text editor of some kind.