You work as a Chief Security Officer for Tech Perfect Inc. The company has an internal room without any window and is totally in darkness. For security reasons, you want to place a device in the room. Which of the following devices is best for that room?

The critical factor in the scenario is the room's environment: "totally in darkness." A photoelectric motion detector is an active sensor that operates by transmitting a beam of light, typically infrared (IR), from an emitter to a receiver. An alarm is triggered when an object passes through and interrupts the beam. Because this device generates its own light source (the IR beam), its functionality is completely independent of ambient light conditions, making it the most suitable and effective choice for a completely dark room.

B. Badge: A badge is an authentication token for an access control system to permit or deny entry; it does not detect unauthorized presence within the room.
C. Closed-circuit television: A standard CCTV camera requires visible light to capture an image and would be useless in total darkness unless it is a specialized thermal or infrared camera with an IR illuminator.
D. Alarm: An alarm is an annunciation device (e.g., a siren or light) that signals a security breach; it is not a sensor and requires a trigger from a separate detection device.

1. U.S. Army Corps of Engineers. (2020). Unified Facilities Criteria (UFC) 4-021-02: Electronic Security Systems.

Page 3-6

Section 3-4.2.2

Infrared Photoelectric Sensors: This section describes photoelectric sensors as "active sensors [that] project a narrow beam of pulsed infrared energy from a transmitter to a receiver." This active projection principle confirms its operational capability in complete darkness.

Page 3-11

Section 3-5.1

Closed Circuit Television (CCTV): This section discusses camera performance relative to light

stating

"The ability of a camera to produce a usable video image is dependent on the amount of light reflected from the scene..." It further details the need for supplemental lighting (visible or IR) for low-light conditions

confirming a standard camera's ineffectiveness in darkness.

Page 3-2

Section 3-2

Intrusion Detection System (IDS) Components: This section distinguishes between sensors (detection)

control units (processing)

and annunciation devices (alarms)

clarifying that an alarm is a separate component from a detector.

2. Garcia

M. L. (2007). The Design and Evaluation of Physical Protection Systems (2nd ed.). Butterworth-Heinemann.

Chapter 5

Intrusion Sensing: This chapter details various sensor technologies. It explains that active infrared sensors (photoelectric beams) are effective because they create their own "monitored energy

" making them independent of environmental lighting. In contrast

it notes that standard CCTV is a passive sensor that relies on available scene illumination.

3. Sennewald

C. A.

& Baillie

C. (2015). Effective Security Management (6th ed.). Butterworth-Heinemann.

Chapter 11

The Alarm System: This chapter explains the fundamental components of an alarm system

consistently identifying three parts: the sensor (detector)

the control panel (circuit)

and the annunciator (alarm/notification). This supports the reasoning that an "alarm" by itself is not a complete or functional security device for detection.