Author: Jonas Bilinkevicius 

I have a tab control with a tab called "Polic&y Info" with the ALT-Y key set to 
switch to it. If I am on a TCheckBox on any tab and press only the "Y" key, the tab 
control switches pages.

Answer:

This is nothing specific to a checkbox, it is standard Windows behaviour. If the 
control having focus does not process character input then ALT is not needed to 
have a character act as an accelerator. To fix this, add a handler for 
CM_DIALOGCHAR to your form:

1   private
2   { Private declarations }
3   
4   procedure cmDialogChar(var msg: TCMDialogChar); message CM_DIALOGCHAR;
5   
6   procedure TForm1.cmDialogChar(var msg: TCMDialogChar);
7   begin
8     if ((msg.keydata and $20000000) = 0) then
9       msg.result := 1 { ALT not down, eat key }
10    else
11      inherited;
12  end;