How spy on someone using a lightbulb as a remote microphone

This video was made a group of security researchers based at the Ben-Gurion University of the Negev and the Weizmann Institute of Science in Israel. The Lamphone, as they call it, is intended as an alternative method of eavesdropping on private conversations without having to compromise a device with malware. In their tests, the researchers were able to accurately monitor audio, including speech and music, from about 80 feet away; they think they could amplify that range with some better hardware, too.

And all it takes is a few simple tools:

Telescope - This piece of equipment is used to focus the field of view on the hanging bulb from a distance.Electro-optical sensor - This sensor is mounted on the telescope and consists of a photodiode (a semiconductor device) that converts light into an electrical current. The current is generated when photons are absorbed in the photodiode. Photodiodes are used in many consumer electronic devices (e.g., smoke detectors, medical devices).Sound recovery system - This system receives an optical signal as input and outputs the recovered acoustic signal. The eavesdropper can implement such a system with dedicated hardware (e.g., using capacitors, resistors, etc.). Alternatively, the attacker can use an ADC to sample the electro-optical sensor and process the data using a sound recovery algorithm running on a laptop.

So basically, a laser; something to point it at (like a light bulb); and something to convert the sound. It works with LEDs as well as incandescent bulbs, too.

Here's how Davey Winder at Forbes describes the process:

Fluctuations in air pressure on the surface of the hanging bulb are created by the sound of conversation, or music, and make a hanging bulb vibrate.