Which of the following is a sign that a Holter monitor may not be functioning properly?

A Holter monitor is a portable device used to continuously monitor the heart's electrical activity over a period of time, typically 24 to 48 hours. One key aspect of its effectiveness is the proper attachment of the leads to the patient's skin. When the leads become detached, it can result in incomplete or inaccurate recordings of the heart's activity. This can lead to missed arrhythmias or other critical heart events that the monitor is designed to detect.

In contrast, if the monitor is securely in place and the patient reports no discomfort, it suggests that the device is functioning as intended. Furthermore, while a low battery can affect the monitor's performance, the immediate sign of malfunction in terms of data collection and quality is primarily the detachment of the leads. Therefore, the detachment of leads is a clear indicator that the Holter monitor is not functioning properly, as proper lead attachment is essential for accurate monitoring.