How do I stop pda machine switching to a different screen ?

[SpacePhoenix]

There's an image there of one of the PDAs. Press the 3rd icon at the bottom (the one that kinda resembles a paragraph of text) and you'll the see the option to lock the application

Aaarghh! That's even worse! You have to put in your pin every time, and that just takes it back to normal ie You scan, it beeps once, you look and it says Ad-Hoc, you scan again, no beep, you look, it's minimised, etc.

Realistically then you're just going to have to put up with the PDA switching screens