I’ve set the Hall setting to 1 in /usr/share/csd/settings.d/10-hw-settings.ini. I’ve tried placing a magnet about 1 cm to the left of the volume button but no dice. I’ve used the same magnet with my XA2 and it works on that.
Is there anything else I can try?
On my device this setting is 0 and the sensor works.
It’s only to make the Hall test available under csd, not sure why it’s disabled by default
A bit OT but was is the TouchAuto setting?
That test fails every time.
I’ve tried a magnet all over the screen and cannot get any reaction.
Is there a Hall Effect sensor or not? If so how do you activate it?
It’s there, but the bug report on github suggests it is officially disabled by sony (or was and no longer is? No reply from sony so your guess is as good as mine). If you can’t get the test to pass, it’s likely faulty (or wrong magnet and/or positioning, but it should trigger rather easily and will lock the device even without running csd)
Edit: for me it triggers more easily with magnet applied to the back of the phone rather than to the front/screen
For me it has always worked directly under the camera.
Well, well, well.
When I remove the phone from the case and place a magnet beside the bottom or just to the side of the bottom of the camera window on the back of the phone the screen turns off and on.
If I run the CSD test I get a pass for the Hall Effect Sensor. Now to find a way to be able to trigger it with the flap. Hmmmmm.
It seems the magnet I was using for testing may not have been ideal.
I found out where the magnet was on the case for my XA2 and then placed that to the left of the volume button on the front of the phone and I was I able to trigger the Halle Effect sensor and turn the screen on and off. I have cannibalised the magnet out of an old case and fitted it to the case I bought and now have the screen turning on when I open the flap. 
This is an irretating bug. I’m using MagSafe to attach my Xperia X10 III next to wheel.
The display goes off always and I need to press power button to get display back on.