Hand Grab interactable: How can i trigger an event when i grab an object

I'm developing a mixed reality game where you can grab floating objects and they give you information when you grab them with your hands, and the info goes away when you release them. 

I know how to make them grabbable, i've been able to make them interactable, but i'm not sure how to trigger an event when an object is grabbed! I've looked everywhere, any help would be greatly appreciated.