The first person (with the Ancient gene) to touch it activates it, and it imprints on that person so that that person is the only one who can use it. How it physically attaches to a person - Ancient velcro, as far as I can tell. :P

They seem to change the rules on that imprinting thing in S3 (but it won't make a difference in my story). Ancient velcro! Hah! That's what I suspected! :-)