Compare byte value to bytea column
I have a bytea field with the value \x11AA22BB. The comparison to a
  byte value of AA should be true


It seems you're looking for the position function, knowing that it will return 0 if the byte is not contained in the string:

select position('\xAA'::bytea in '\x11AA22BB') &gt; 0 AS contained;

 contained 
-----------
 t


If the byte value is stored in an integer, set_byte can be used to place it into a bytea:

select position(set_byte('\x00', 0, 170) in '\x11AA22BB') &gt; 0;