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This chapter is from the book

This chapter is from the book

Physical Devices

The six major physical components of a home security and surveillance system are described in this section. Although some designs include additional components for enhanced performance or custom installations, the physical devices described here are considered the basic building blocks for a security and surveillance system that will provide adequate protection from intrusion. The essential physical assemblies include

  • Keypads

  • Sensors

  • Security panels

  • Cameras

  • Monitors

  • Switchers


The keypad is the device used by the home residents to initiate commands for control options and observe the status of the security system. As shown in Figure 3.3, it usually contains an alphanumeric keypad and LED displays that indicate the status of the alarm system.

Figure 3.3Figure 3.3 Keypad.

The keypad is used to arm and disarm the system and often includes a panic switch by which the alarm can be triggered instantly in an emergency situation. The alarm can be silenced by the owner by entering the correct coded sequence of numbers on the numerical keypad. The keypad is typically installed inside the home near a door that is most frequently used by the residents. A programmed delay is included as a feature of most systems to enable the users to enter and disarm the system within a fixed delay period (normally 30–45 seconds). The same fixed delay is also used to allow the user to arm the system and exit the home within the fixed delay period. Keypads can also be used to bypass certain areas.


The bypass function is used to arm the system but disable selected zones or motion detectors inside the home when the family is present. Residents often desire to secure the perimeter area of doors and windows after retiring for the evening but need to bypass interior area motion detection sensors that are activated only when the home is not occupied.


Sensors are designed to protect both the perimeter and the open spaces inside the home. As mentioned earlier, perimeter devices primarily protect doors and windows. The most common perimeter sensors are magnetic door switches, window vibration detectors, and window acoustical detectors. Space protection sensors called motion detectors cover interior rooms and hallways and can detect an intruder who has been able to defeat a perimeter device. Exterior motion detectors and motion-activated security lights are also used. The following paragraphs describe the types of sensors required in basic home security and surveillance systems.

Door Switches

Door switches work on a basic principle of a two-part magnetic switch. A switch that is sensitive to a magnetic field is mounted on the fixed structure (frame), and wires from the switch are routed through the wall to the control panel. A magnet is mounted on the door in a position where it is in close proximity to the switch when the door is closed; this also keeps the switch closed. Opening the door moves the magnet away from the switch and causes the switch to "open," which is sensed by the central control panel and activates an alarm. Magnetic switches are available as normally open (NO) or normally closed (NC) to accommodate different wiring designs and controller options.

Window Acoustic and Vibration Detectors

As you learned earlier, window sensors are used to detect the sound of breaking glass. Large glass doors such as patio doors are usually protected by magnetic switches. Windows in the home can also be protected by magnetic switches if they can be opened; however, glass break detectors are recommended by most home security contractors to protect against an intruder entering through a broken window.

Glass break detectors are available in either vibration type or acoustical type. The vibration type is mounted on the glass or on a nearby wall.


Security system magnetic switches are designed for both normally closed (NC) and normally open (NO) options. An NC switch opens when the magnet is moved near the switch, and an NO switch closes when the magnet is moved in close proximity to the switch. This enables magnetic sensor-type switches to be used with various types of security system designs. Sensor door switches wired in parallel use NO contacts so that any closure of the contacts in the circuit activate an alarm condition. Series circuits use NC magnetic switches where any opening of a switch results in an open condition for the circuit, which triggers an alarm condition by the controller.

Motion Detectors

Motion detectors work by detecting the changes in the infrared energy in an area. Because these devices do not emit any energy, they are called passive infrared (PIR) detectors. PIR detectors use a lens mechanism in the sensor housing to detect a change in infrared energy across the horizontal sectors covered by the sensor. This type of detector is insensitive to stationary objects but reacts to rapid changes that occur laterally across the field of view. They are the most common and economical type of motion detectors and are available in standard, pet-friendly, and harsh-environment (outdoor) models. An example of a motion detector for interior use is shown in Figure 3.4.

Figure 3.4Figure 3.4 Motion detector.

Security Panels

Security panels provide several functions to coordinate the operation and management of a security system. They can include an integrated keypad or LED indicators. Most designs include a power transformer for converting the AC voltage to a DC voltage for the sensor loop and contain a rechargeable battery for backup if the commercial power fails. A terminal strip provides for the connection of the wiring that connects all the sensors to the controller as well as the external telephone line. Most designs include a printed circuit board containing all the electronics and a microprocessor. It also connects to and controls the siren that is activated when an alarm condition exists.

Security panels are known by numerous names, such as central control box, control panel, alarm panel, and interface panel. They all perform similar functions including controlling and monitoring sensor status, providing power to the system, connecting the telephone line to the monitoring station, and handling the programmable options for the system.


Surveillance systems for the home use video cameras that convert the image into a video composite or S-video signal for display on a video monitor. The best type of camera for home systems uses charged coupled device (CCD) technology. These cameras have high resolutions, low operating light, less temperature dependence, and high reliability. A typical CCD camera used in video surveillance systems is illustrated in Figure 3.5.

Figure 3.5Figure 3.5 Video surveillance camera.

Camera Resolution and Sensitivity

The two important specifications for cameras are the light sensitivity rating and the number of lines of resolution. The resolution of a camera is a measurement of the horizontal lines it is capable of generating. Most standard TVs and VCRs have a resolution of fewer than 300 lines, but video monitors can have a resolution as high as 800 lines. Surveillance cameras come in a range of costs and are available with 300–500 lines of resolution. Higher resolutions make distinguishing fine details and recognizing people at a distance easier.

The amount of light required to obtain a reasonable image is called the lux rating. 1 lux is approximately the light from one candle measured from 1 meter. Typical camera ratings range between 0.5 and 1.0 lux.


Monitors are cathode-ray tube display systems similar to computer display systems. They are used to display video information processed by the camera. Coaxial cable is used to connect the camera to the monitor that can be located in any area selected by the user. Monitors do not have a TV tuner and usually have better video resolution than standard television receivers. They can also be connected to programmable switchers that receive input from several cameras and show multiple images on a single monitor.

Closed circuit TV (CCTV) monitors are available for black-and-white or color display depending on the resolution and camera selection. Black-and-white monitors have resolutions in the range of 700–1000 lines, whereas color monitors are available with 350–400 lines. CCTV monitors are designed for extended 24-hour-per-day operation.


Video surveillance systems for both home and commercial business use are referred to as closed circuit TV (CCTV) systems. The name is derived from the type of the system used for transmission over a closed circuit or private transmission circuit rather than a standard television broadcast system. CCTV is also used in a wide variety of applications for schools, business video conferencing, retail store surveillance, and gambling casinos.


Switchers are devices used with multiple camera systems. Although primarily used in commercial building security and surveillance systems, they can be scaled to fit the needs of a home security system. They enable several cameras to be used with a single monitor. The switcher can be programmed to cycle through all the cameras in a surveillance system or dwell on each camera for a specified length of time, usually in the range of 1–60 seconds. Exterior sensors can detect movement and cause cameras to start recording the image on a VCR.

Quads are special devices that enable the viewer to simultaneously record and monitor four cameras. It does this by splitting your screen into four sections. The normal configuration for connecting a quad switcher with a sensor and a VCR is shown in Figure 3.6, which illustrates the connections between a quad, a monitor, and four surveillance cameras. The monitor can view all four images at the same time.

Figure 3.6Figure 3.6 Quad camera switcher.

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