Seth Godin has a good idea about protecting our valuable electronic devices from being misplaced, by an alarm for lack_of_proximity.
I would also really like to see a feature where it would be possible to track down lost or stolen cell phones but something to avoid it happening altogether is even better.
An example service for laptops is lojack. Either the valuable portable device needs this type of service or it needs to be inexpensive enough that it can be disposable.
Dell offers lojack as part of a bundle for its laptops.