You can find out what people have said in a room by creating a homemade spy listening device. Leaving a voice-activated recorder hidden in the room allows for easy eavesdropping. Such recorders are light on power requirements and can usually stay in a room for several days without refreshing the batteries. The hours of silence in a room will not be recorded, offering further efficiency. The trick to voice recording is always going to centre on the microphone. This method shows how to hide a mini-condenser microphone in a bouquet of plastic flowers.
Disassemble a multimedia computer microphone using a utility knife. These microphones often come with a flexible arm and free-standing plastic base. Cut carefully around the end of the microphone head and peel back the plastic until the mini-condenser microphone is revealed. Retrieve the microphone from the arm's plastic housing and the wire leading to its 1/8-inch mini-stereo plug. Discard the arm and base.
Connect the mini-condenser microphone's 1/8-inch plug into a voice-activated digital recorder's headphone jack. Turn the recorder on and set it to voice activate. Turn the volume up high.
Place the recorder in a dark flower vase. Make sure the vase is opaque to the point the recorder cannot be seen inside it. Take care not to bump it on the way down. Hold the microphone outside the vase.
Place bouquet of plastic flowers in the vase. Attach the microphone below one of the flowers, using clear cellophane tape. Allow the cord from microphone to fall back into the vase.
Arrange the flowers so the microphone is hidden from casual view at all angles. Keep the flower with the microphone near the middle of the bouquet so other flowers and leaves help shield it from sight.
If you pick up too much extraneous noise, consider lowering the gain on the digital voice recorder. Try different locations in the room and different angles for the microphone to improve results.
Be aware of the laws about the use of recording devices in your area. Some states do not permit the recording of conversations without the knowledge and consent of all parties.