Morse code is one of the most known codes in the world. Here's how to make an inexpensive telegraph to send messages in code. I did this for a science project. I got a low mark cause it dosen't qualify as a "simple machine". I hope it goes to better use out here.
Step 1: Connection
I. Connect the negative wire of the battery to the negative wire of the buzzer
Step 2: Buzzer
II. Attach an alligator clip to the positive wire of the buzzer and the battery to the clothes pin
Step 3: Two Way Calling
If you want to chat to someone with a telegraph, make another one and connect the buzzers with a long wire. Then when you type a message your buzzer and the buzzer at the other telegraph will make the same message.