Brief Case Alarm?

I've heard of an alarm for brief cases that has two parts, one part goes inside the case, the other part you wear on you and an alarm goes off if the two are too far apart - like if someone tries to walk off with your case or you try to walk off without it.

I've checked the usual sources to no avail, has anyone heard of such a beast or know where I can get one.

Cheers

Paul