Monster ability: Scent Magic

[Val'bryn2]

Doing a little world building and came up with a moderately interesting idea for q twist on certain monsters, which evolved into a new monster ability I want to give to ogres. What kind of CR boost, if any, would you think is fair for an ogre with the scent ability, but only towards magic within 30 feet. They can smell creatures with spells or spell-like abilities, or magic items. The logic behind it would be they are the male equivalent of hags, or rather they are male hag-children, undergoing the change that turn their sisters into hags.

[DeathlessOne]

No actual CR boost needed. Scent, by itself, isn't that powerful of an ability.

[Darigaaz the Igniter]

And here I thought, by the thread title, you were giving them smellcasting.