Security countermeasure costs

1. Give an example of a situation in which a motion-detection alarm might be deployed effectively. Under what circumstances would an ultrasonic system be chosen over a radio frequency system?

2. Describe how passive infrared detectors operate. What environmental variables must be considered to assure proper operation?

If a security countermeasure costs as much as, or more than, the loss being protected against for a given period, does it follow that the security measure should be discontinued because it is not cost-effective?