A microphone that is installed on a common wall adjacent to the target area is known as a:

A microphone installed on a common wall adjacent to the target area is referred to as a contact microphone. This type of microphone is designed to pick up vibrations or sounds directly from the surface it is attached to, making it particularly effective in environments where audio sources are present but may not be easily accessible or visible. In this case, mounting the microphone on a wall allows it to capture sounds from the adjacent area effectively, as it can detect the vibrations transmitted through the wall.

Understanding the application of contact microphones is important, especially in security and surveillance contexts, where discreet monitoring of conversations or activities is needed without direct line-of-sight access to the sound source. This design maximizes the microphone's ability to pick up clear audio by utilizing the structural elements of the building.