Countering Light Bulb Eavesdropping

Q. "How to prevent light bulbs from being used as pickups for speech?" (meaning, being used as part of an eavesdropping system)

A. The easiest way, of course, is to keep the bulb turned off, however, I know that's not what you mean.

The second best way is to make sure there is no way for the bad guy to see the light bulb. Most attacks require accessing the bulb's variations in light so they can be remotely demodulated. (See Leon Theremin's invention.)

Some bulb attacks are made possible because additional electronics are placed inside the bulb (cameras, transmitters, microphones, etc.). The easiest countermeasure to this is to replace the bulbs with bulbs you purchased from a local Home Depot / Lowe's type store. Mark the bulbs when you install them, then check periodically to make sure they haven't been switched out.

Also, be sure to check the fixtures and wiring paths for attached microphones and modulation circuitry. Cut the power while doing these things.

These are not high-tech countermeasures, but they are effective.

Hope that helps,
Kevin