With the 'pressureplatetrigger' attribute you can set what can trigger the pressureplate.
Valid values are 'all', 'player', 'monster', 'animal', 'creature', 'item', 'noplayer', 'nomonster', 'noanimal', 'nocreature', 'noitem'.
Default value: all
pressureplatetrigger="all";
pressureplatetrigger="noplayer";