## Core Concept
The question tests the knowledge of devices used during cardiopulmonary resuscitation (CPR) to monitor the effectiveness of chest compressions. The focus is on a noninvasive method to assess the quality of external chest compressions.

## Why the Correct Answer is Right
The correct answer, **C.**, refers to a device known as a "piezoelectric sensor" or more commonly, a device that utilizes technology to assess the depth and rate of chest compressions during CPR. One such technology is the **Resusci Anne** or more specifically for feedback, devices like the **Lifepak** or **Q-CPR** systems which often use accelerometer or piezoelectric sensors to provide feedback on the rate and depth of chest compressions. These devices are noninvasive and can be placed on the patient's chest to monitor the compressions.

## Why Each Wrong Option is Incorrect
- **Option A:** This option is incorrect because it does not correspond with known devices for CPR feedback.
- **Option B:** Similarly, this option does not accurately represent a device used for monitoring chest compressions during CPR.
- **Option D:** This option is also incorrect as it does not accurately describe a device used for the purpose stated.

## Clinical Pearl / High-Yield Fact
A key point to remember is that the use of **feedback devices** during CPR can significantly improve the quality of chest compressions by providing real-time information on rate and depth, potentially improving patient outcomes.

## Correct Answer Line
**Correct Answer: C.**