In a 30x30 frame building, which type of motion detector is considered least effective?

In the context of detecting motion within a 30x30 frame building, the photoelectric motion detector is regarded as the least effective option due to its operating principles and limitations. Photoelectric detectors work by using a beam of light that, when interrupted by an object or motion, triggers an alarm. This method can be influenced by various environmental factors, such as dust, insects, and changes in light conditions, which may lead to false alarms or an inability to effectively cover larger areas or certain types of movement.

In comparison, passive infrared (PIR) detectors are designed to detect changes in infrared radiation that come from warm bodies, making them effective in various settings, especially for human movement. Microwave detectors emit microwave signals and can detect movement based on the reflection of those signals, often providing more comprehensive coverage. Dual technology detectors combine both passive infrared and microwave technologies, increasing their reliability by reducing false alarms and improving detection capabilities.

Given the nature of the building's size and standard motion types within, the effectiveness of the given technology varies, but photoelectric detectors typically have limitations that may hinder their performance in broader applications, thereby making them the least suitable choice in this scenario.