How to Prevent Wireless Microphone Eavesdropping

Step 1 – Know Your Microphone

Basically, a wireless microphone is a miniature radio station worn by a public speaker, presenter, or musician. The sound of the person’s voice and/or musical instrument is transmitted to a nearby radio receiver, amplified and played through loudspeakers so the audience can hear more easily. In some cases the audio is also used to make a recording or is transmitted to a select remote audience.

Unfortunately, radio transmissions do not stop at the receiver. Wireless microphones can transmit for distances of 100 feet to a mile depending upon the type of microphone and terrain. Any receiver tuned to the same frequency can receive the signal, if it is an FM analog signal.

FM analog modulation is used by all older wireless microphones. Inexpensive wireless microphones currently being sold are also FM analog types.

Eavesdropping on a specific meeting is only one danger. Presenters often don’t know, or forget, lavaliere microphones continue to broadcast when they are off stage. Only the receiver may be turned off. This means that side comments, hallway and bathroom conversations will still be intercepted. Even when the presenter removes the microphone, it may not be turned off. So beware, commercial wireless microphones are designed to be sensitive, and they broadcast crystal clear audio.

When targeting off-site meetings, for example, the opposition will set up radio receivers and recorders in one of the hotel’s rooms, or in an unoccupied car parked nearby, as demonstrated in this 2-minute video. (You may also use the QR code to access it.)

These outsiders are betting you will use wireless microphones, and that you will make a variety of other simple security mistakes. You will never see them.

There are three basic types of wireless microphone transmissions: FM Analog, Digital, and Digital Encrypted.

• FM Analog Microphones

FM analog transmissions are the easiest to intercept. All that is required is a radio receiver tuned to the same frequency.

FM analog wireless microphones look similar to other types of wireless microphones. Clues that you may be using an FM analog microphone include: it’s an older and/or less expensive model.

A quick internet search of the model number can confirm the type. Many FM analog microphone specification sheets do not mention their transmission type as being FM analog, no surprise there. They also don’t mention encryption. Price is another good indicator of security. If it is inexpensive, it is probably an FM analog model.

• Digital Microphones

Eavesdropping on digital transmissions is difficult, but not impossible. When intercepted, the signal sounds like static instead of a clear voice. This is because the transmitter is communicating with the receiver digitally. This eliminates random eavesdropping. The receiver then converts the digital signal back to analog so it is intelligible.

If a determined eavesdropper is aware of the make and model number of the system being used they can simply purchase a like receiver for interception and demodulation.

Identifying a true digital wireless microphone can be tricky…

Digital Doesn’t Always Mean Secure

A digital wireless microphone can mean several things…

Some manufacturers label their FM analog wireless microphones as being digital, without further explanation. When pressed, they admit digital only refers to the circuitry, not the transmission; this is a very deceptive marketing practice.

Honest manufacturers use the digital label to mean the transmission is digital. While this increases security due to the steps needed to demodulate the transmission, absolute privacy cannot be fully assured.