Which of the following is the most expensive method to test for radon?

Active monitoring systems are considered the most expensive method to test for radon due to their advanced technology and capabilities. These systems involve electronic devices that continuously measure radon levels in real-time, providing immediate feedback on radon concentrations. This ongoing data collection requires more sophisticated equipment, which tends to have higher initial costs and may also involve ongoing maintenance and calibration expenses.

In contrast, short-term tests and passive detectors generally have lower costs associated with their simplicity and ease of use. Short-term tests, while they provide quick results, are limited in their scope and duration of measurement. Passive detectors are very cost-effective as they do not require any additional power source and can be left in the testing environment for extended periods without the need for complex technology.

Long-term tests, while potentially more expensive than short-term options, still do not reach the complexity and operational costs associated with active monitoring systems. As such, the significant investment in equipment and technology associated with active monitoring systems solidifies their status as the most costly method for testing radon levels.