Cool use of Smart phones in the classroom

In their grade 12 summative students had to design, build and test a complex (series/parallel) circuit that included 2 IR LEDs. The big question of course was "How do we know it is working." Simple, turn on your smart phone camera and look at the LEDs through the camera. Since modern CCDs see into the near infra red the students could see the magically glowing LEDs on their phones when, to the naked eye, they appeared to be off.