QR codes

 Your students have probably seen these images around and might not know why they are becoming popular for smart phone scanning ... and possibly dangerous.  Students figure out the number of permutations of symbols that are possible with these 2-d scanning codes and compare that capability  to the capacity of ordinary UPC barcodes.   This activity might open student's eyes to some of the marketing that surrounds them and help them become aware of some possible dangers … all while engaging in mathematics.