You will be taught how to make a device that depends on laser to hear voices inside closed room from 100 meters distance, just by pointing the device laser to a window! Its a simplified way and based on same idea of military spy devices
The other thing you will be taught is how to transfer music and voices through laser, usually to transfer such files we use bluetooth or cables, but how about sending voice at speed of light? (literally)!!
You will be amazed of how cheap and simple both projects are! they both together will surely cost you less than 50$ for high quality hardware if you already have a PC or laptop.
Will always offer step by step here, and always available for help if anything goes wrong!