Step 8: Alternate construction and Theory
Instead of using a battery and solar resistor, you could just use a small solar panel. However, these are more expensive and tend to break more easily.
Theory: It may be possible to bounce the laser of glass behind which a conversation is occuring (such as a window) and pick up the sounds on the reciever, but I've yet to test it. Please let me know if anyone has tried this or has a better way to do this.