Which type of microphone is characterized by requiring no power source and being difficult to detect?

The dynamic microphone is characterized by its ability to operate without an external power source, making it a popular choice for various audio applications. It uses a simple electromagnetic principle where sound waves cause a diaphragm to move, generating an electrical current that corresponds to the sound. This mechanism does not require battery power or phantom power, which is typically necessary for other types of microphones.

Additionally, dynamic microphones are known for their ruggedness and ability to handle high sound pressure levels, making them particularly effective in live sound settings. Although dynamic microphones may not be the most discreet option available, their passive nature means they can still be less detectable compared to powered options, especially when considering the absence of external cables or power sources.

In contrast, other microphone types mentioned often rely on power for operation. For example, a parabolic microphone typically utilizes powered components to enhance sound capture from specific directions. Contact microphones may depend on a power source for amplification, and the term "infinity microphone," which is less commonly used in professional audio terminology, may refer to more specialized designs that might also involve power requirements.

Thus, the dynamic microphone stands out as the answer due to its independence from external power while maintaining effective sound capture capabilities.