A system monitoring device must have a label that includes what information?

The correct answer focuses on the necessity for a system monitoring device to have a label that includes instructions on interpreting readings and actions for failures. This is crucial because such information enables users to understand what the readings mean, how to respond to different levels of radon concentration, and what to do in case of device failure or malfunction.

Clear instructions help ensure that the monitoring device is used effectively and safely. Without this critical information, users may misinterpret readings or fail to take necessary actions in response to elevated radon levels, possibly exposing themselves to health risks. Furthermore, an understanding of the readings is essential for maintaining effective radon mitigation efforts and for making informed decisions about the indoor air quality of a residence or building.

In contrast, simply including the installation date or general operational guidelines does not provide the same level of actionable information necessary to respond appropriately to the data the device provides. Not requiring any specific information at all would not meet safety and operational standards. Hence, the emphasis on having comprehensive instructions on interpreting readings and addressing potential failures is what makes this option the most appropriate choice.