Washing Machine Feature: Detect Electronics in the Load

My daughter had a good design idea today--she said that washing machines need a feature where they detect if an electronic device is in the tub. Obviously the point here is to prevent iPods, cell phones, etc from being left in pockets and tossed in the wash (has happened to her once). That really is a half-decent idea...if the machine had a detector for cell phone and wi-fi signals. I guess false positives would likely be a problem (cell phone in my pocket while loading the laundry).