Without any sort of official "Now we're starting science, and we are learning to...", I discovered an envelope marked Top Secret, and asked who it was from. With no answers from the class, I dumped a flash drive into my hand, plugged it into my computer, and found this video:
The plot is a little thin, but it did the trick.
After I had their attention, I reached back into the envelope, and pulled out a class set of articles about Samuel Morse with Morse Code on the back. How convenient! I quickly read the article to them to build a some background about what they were doing, focusing on the Morse Code section.
I was going to demonstrate how the dots and dashes could be transmitted with sounds, but by the time I was done reading, I had a handful of kids that had already decoded the messages, so I chose to let them work.
Once they had written their name in Morse Code, I had them come up to get LED's, wires, and batteries, and show how to make their names with those. I expected the LED's to work with single batteries, so I didn't have enough supplies for everyone to work in pairs, so they mostly worked in groups o 3. This wasn't meant to be quite so heavy of a circuits review, so if I had some kind of kit or something, I probably would have used it. Or better still, this would be a great way to unify an electricity unit, giving students a culminating activity to work towards.
Once they were able to send a basic message in Morse code, they worked with their groups to develop a new code that had to use at least two LED's. I expected them to use the ideas behind Morse code, I just made sure they went beyond substituting long for one color and shorts for another.
Once they had their alphabet worked out, I encouraged them to practice sending a receiving a few messages. When they were sure they were ready, I had the sender in each group choose an index card with a name written on it. Their final test was to successfully transmit that name to their partner who was at least 10 feet away.
For assessment, I made this a performance task. If they were able to send and receive the message successfully, they earned 4 points, 3 if they made some errors in the sending and receiving, and 2 if they weren't able to develop a code with 2 LEDs.