Final answer:
The best two choices for motion detectors in a volatile environment are passive infrared detectors and microwave detectors.
Step-by-step explanation:
In a volatile environment, the best two choices for motion detectors would be passive infrared (PIR) detectors and microwave detectors. PIR detectors detect infrared radiation emitted by living beings, while microwave detectors use radio waves to detect motion. Both these detectors have advantages and disadvantages, and the choice depends on factors like the specific environment, budget, and desired level of sensitivity.