Two points. I was flying from London to New York a couple of years ago. My two suitcases each had an iTag within. As we were taxiing up to the airbridge at JFK, my iPhone indicated that my two cases were still at Heathrow - a big surprise. Then came the announcement that some clown had packed fireworks in his case and as a result ALL our luggage had been removed prior to takeoff.
I got a new car 9 months ago and I have placed an iTag under the carpet in a rear footwell.