You might not need special sensors or old-fashioned inspections to tell whether food has gone bad. If MIT has its way, the tags you already find on your food might do the job. Its researchers have developed a wireless system, RFIQ, that detects potential food contamination based on minute changes in the signals emanating from the RFID tags you often see on containers. As different materials absorb different amounts of the tags' electromagnetic frequencies, you can use a reader to spot changes in response signals and identify food contamination. If a foodstuff dries out, for instance, you'd notice a different signal than when it was still moist.