Have you ever needed to hear a conversation in a room you are unable to access or bug easily? If so, and if that room has a window, you can using a laser microphone.
A laser microphone is a device that uses the vibrations of a window or similar pane of glass or plastic to record sounds near said window. A laser is pointed at a window and a photocell is placed where the laser's reflection lands. That photocell is then connected to a recording device. The vibrations of the eindow causes slight movements in the laser's reflection which, in turn, cause small fluxuations in the photocell microphone's current. This may seem complicated but it can be done cheaply and easily.
Step 1: Things Needed
The things you need for this build are very easily obtained and cost me about $10.
Soldering gun( or just electrical tape if you're being really cheap)
Scissors( if you're using headphones)
A laser pointer $1.50
A photocell $.30
A bad pair of headphones or, as I used, a speaker cable ending normal headphone jack $3.80
A tripod $0.00( already had one and isn't needed)
Recording device or computer with recording software