Lenovo makes some great laptops, like their ThinkPad T series.
But who's brilliant idea was it to "hard" wire the Fn-Tab key combo at a low level to activate the Windows Magnifier?
This annoying behaviour can't be remapped away with AutoHotKeys.
Lenovo's Vantage program calls them Hidden Keyboard Functions. They're aware some people have a tendency to mistype Fn for Ctrl, so they offer a "Fn and Ctrl key swap" option instead.
Two ways to disable Fn-Tab Magnifier behaviour
(1) Disable permanently by changing the Magnify app's name
You can take file ownership of the Magnifier app, then change it's name from Magnify.exe to something else (e.g. Magnify.exe.bu as a backup).
That way, Fn-Tab can't find the Magnify app!
But Windows's own key combo won't find it either! Congrats, you've disabled the Magnify hotkey permanently.
Detailed instructions can be found elsewhere [2] labelled as "method 2" (different than my # 2 below).
I don't like this method because I still want the Windows hotkey to bring up the Magnifier.
(2) Disable only the Fn-Tab hotkey
Inspired by a similar question from way way back [3], I found out the Fn-Tab hotkey will open any app who's path is entered into a specific Windows Registry entry!
Specifically, this Registry entry:
HKEY_LOCAL_MACHINE\SOFTWARE\Lenovo\ShortcutKey\AppLaunch\Ex_13\UIAccess
The key name "File" by default has the data value:
%SystemRoot%\system32\magnify.exe
Well if you change that to:
%SystemRoot%\system32\magnify.exe.bak
Then Fn-Tab won't find the magnify app and won't do anything! In fact, you should be able to make Fn-Tab launch any app you want using this technique!
If you're trusting and lazy, and want an easy way to enable or disable the Lenovo Fn-Tab behaviour, save the following into text files and change the file extension to .reg so that you can double click the file to make the above registry edit for you:
EnableLenovoFnTabMagnify.reg
Windows Registry Editor Version 5.00
[HKEY_LOCAL_MACHINE\SOFTWARE\Lenovo\ShortcutKey\AppLaunch\Ex_13\UIAccess]
"File"=hex(2):25,00,53,00,79,00,73,00,74,00,65,00,6d,00,52,00,6f,00,6f,00,74,\
00,25,00,5c,00,73,00,79,00,73,00,74,00,65,00,6d,00,33,00,32,00,5c,00,6d,00,\
61,00,67,00,6e,00,69,00,66,00,79,00,2e,00,65,00,78,00,65,00,00,00
"Parameters"=""
DisableLenovoFnTabMagnify.reg
Windows Registry Editor Version 5.00
[HKEY_LOCAL_MACHINE\SOFTWARE\Lenovo\ShortcutKey\AppLaunch\Ex_13\UIAccess]
"File"=hex(2):25,00,53,00,79,00,73,00,74,00,65,00,6d,00,52,00,6f,00,6f,00,74,\
00,25,00,5c,00,73,00,79,00,73,00,74,00,65,00,6d,00,33,00,32,00,5c,00,6d,00,\
61,00,67,00,6e,00,69,00,66,00,79,00,2e,00,65,00,78,00,65,00,2e,00,62,00,61,\
00,6b,00,00,00
"Parameters"=""
References
[1] Fn-TAB brings up Magnifier