If they are worn any closer, the sound becomes bassy. Most lapel microphones these days are wireless. These systems require a radio transmitter and a radio receiver. The transmitter is located in the microphone, or connected to it. Sometimes wireless systems can be more of a problem than they are worth.
Wireless systems are open to interference.
It was quite a surprise, and disrupted the training. The receiver has no way of knowing the speaker's voice from the local trucker down the street. As long as they are both transmitting close to the same frequency, the receiver will pick them up. The trucker may not be tuned into the same frequency, but with the power boosters that are being used today the CB signal gets into almost any frequency. In the training session I moved the receiver closer to where the speaker was and further away from the street.