Click to view game on Amazon
If it's cheaper, I'll probably just buy elastic and make my own headbands, but so you get the idea behind the game, check out the link to the official game on Amazon.
Print out graphs of various trig functions and glue them to index cards. Each kid gets a graph to put in their headband. They should not look at the graph when putting it in the headband. They then have to get clues from their classmates that will allow them to write the equation for the graph. We did this with trig graphs, so they were asking questions like "Does it look more like a sine snake or a cosine cup?", "What is the amplitude? The period?", "Does it have a phase shift or vertical shift?" When they felt like they knew the equation for their graph, they wrote it down and checked with me. I think when I do it again, I'll color code the graphs and put an answer key somewhere to allow them to check their answers on their own. I'd probably have them switch graphs at some point, or come up with enough graphs for each person to do at least a couple.
It was a great activity that the kids really enjoyed. It was much more engaging than just getting several graphs on a paper that they had to write equations for....