A specially constructed microphone that responds only when the protected object is disturbed is known as:

The correct answer is the contact microphone. This type of microphone is specifically designed to capture vibrations or sounds directly from a surface it is attached to or in contact with. When the protected object, such as a wall or desk, is disturbed, the contact microphone picks up those vibrations and converts them into audio signals. This makes it particularly effective for covert monitoring or surveillance, especially in situations where conventional microphones might not be able to capture the necessary sounds due to distance or background noise.

Parabolic microphones are typically used to capture distant sounds by focusing sound waves onto a receiver but are not designed to respond directly to disturbances on a surface. Special audio microphones can encompass a wide range of types and features but do not specifically imply a design tailored to the disturbance of physical objects. Surreptitious microphones, also known as hidden or covert microphones, are intended for discreet use but do not inherently feature the mechanism that triggers a response based exclusively on disturbances of the objects they are monitoring. Thus, the contact microphone is uniquely suited for this specific purpose, making it the right choice.