How Many Security Cameras Do I Need?

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How Many Security Cameras Do I Need?

Home and office security becomes a bigger and bigger issue every year. Personal security has become an issue not only for the wealthy, but for upper-middle class families and medium-to-small businesses as well.

Security cameras have been shown to be an effective deterrent to crime, helping to keep people honest. In addition to their deterrent value, video surveillance systems also provide valuable information to police for the capture and prosecution of the perpetrators of these crimes. In many cases, it is the recording of video surveillance cameras that provides the first lead toward eventual incarceration of perpetrators of many crimes.

When setting up a home or office security system, the ideal camera setup, including how many cameras should be used, depends on the characteristics of the area being surveilled, the type of assets being protected, and the type of security camera being used. Generally, having multiple, overlapping security cameras is best in terms of surveillance effectiveness, although this also increases the cost of the overall system.

Designing an Effective Video Security System

For a video security system to be effective, it needs to provide usable evidence of the crime being committed. This requires careful placement of the cameras in order to ensure that all perpetrators are captured on video. There are a number of key locations where cameras should be installed to ensure the provision of adequate evidence.

Entry and Egress Points

The most obvious and common place to install security cameras is in entry and egress points. Pretty much everyone who comes into the home or office must pass these points, providing an excellent opportunity to capture them on video. This does not mean that all criminals will necessarily enter through the door, especially when robbing a home, but in many cases, the doors are the easiest way to gain access.

Cameras used for entry and egress points should be provided with lenses that provide a narrow viewing angle so that they can capture more detail. This is the best opportunity to capture a clear image of perpetrators' faces. Placement of the camera is critical as well, as it must be done so that there is no way to pass through the entryway without being captured by the camera.

Automatically panning cameras should never be used for entry and egress points. If they are used, they provide a window of opportunity to pass into the building without being captured on video. The point here is to capture everyone.

Traffic Choke Points

Since most criminals are familiar with video surveillance systems, they will expect to find cameras at the entry and egress points. The more intelligent and imaginative will develop ways of avoiding having their faces caught by these cameras, whether by looking away, wearing a wide brimmed hat, or holding something that covers the majority of their face.

To capture the faces of those who are missed by the cameras at the entry points, the next best place for cameras is in any traffic choke points. Once again, these cameras should have narrow-angle lenses to capture detail, rather than wide-angle lenses that cover an area. The lens should be sized to cover the full width of the chokepoint, without extra camera angle being wasted taking pictures of the walls.

Cashiers, Tellers, and Others Who Handle Money

Many robberies are performed directly at the cash register, whether by criminals who come in to rob or by employees stealing from the company. Cameras placed to capture the actions of cashiers and their customers provide another excellent opportunity to capture faces of perpetrators. These cameras need a slightly wider field of view, as the perpetrator may stand in more than one position. At the same time, the camera should be able to capture the actions of the cashier or teller.

Some companies try to use one camera to capture the actions of a group of cashiers and their customers. It is important to remember that the wider the camera angle is and the more information that is being captured, the less detail will be available. While it may be possible to capture a robbery in process on a camera with a wide-angle lens, it may not be possible to positively identify the perpetrator from such a video.

It is better to spend the extra money necessary to have one camera for each cashier or teller station. While this adds greatly to the cost of the system, surveillance camera prices have dropped considerably when compared to prices just 10 years ago.

Key Assets

Any valuables that are highly pilferable should be monitored constantly with video cameras. These would include valuable products for sale, valuable materials for use in a facility, or storage of valuables.

Camera placement in these cases should take into consideration all possible angles of approach, as well as being able to see what the individual does with the valuables. It is important to be able to capture the face of anyone performing any criminal activity, not just see that it is being done. Camera lenses should be selected to cover the entire area, while still providing sufficient detail.

Once again, these should be fixed cameras and not panning cameras. It is important to have these cameras also cover the access route to the camera so that the camera cannot be turned from viewing the assets without the person turning the camera's face being recorded.

Outside Areas

While not as critical as the above-mentioned areas, many businesses and homeowners use outside cameras to monitor and record activity around the building. These cameras are provided with wide-angle lenses in order to capture as much of the area as possible. While this does not provide as clear an image as a narrow camera angle will, it can provide key information, especially if the entrance or choke point cameras are compromised in any way.

While it is common to use cameras on an automatic pan head in these applications, it must be noted that criminals will look for and time the actions of said cameras. If it is possible to gain access without the camera capturing their activities, they will attempt to do so.

A Word About Camera Overlap

One way of creating a very secure video surveillance system is to overlap camera angles. This reduces the possibility of anyone slipping through the system without being seen by one camera or another. However, it greatly increases the cost of the system, as more cameras and more wiring is needed.

As part of designing an overlapped system, it is a good idea to have cameras include the positions of their nearest neighbors in their coverage angles. That way, if someone were to tamper with one camera, it would be caught by the next nearest cameras. This is somewhat complicated to set up, but it can be accomplished by carefully laying out the cameras on a plan of the facility.

Camera Selection for Surveillance Systems

There are a number of different camera types available for installation in a video surveillance system. It is important to select the best type of camera for each application and not just select any camera, thinking that it will be "good enough."

Wired vs. Wireless Cameras

Everything is going wireless these days. It is more convenient, cheaper, and easier to install. However, wireless equipment is not as secure as wired equipment. Any wireless signal, whether from a home's Internet connection or from a security system, can be pirated. For this reason, high-security installations always used hard-wired security cameras. The extra work pays off in greater security.

Conventional vs. Infrared Cameras

Night vision infrared cameras (IR) are very fashionable. Many video security packages come with IR cameras. However, some important issues need to be considered when using IR cameras. First, they do not capture the same level of detail as a conventional camera. While facial recognition is possible with IR cameras, it is more difficult, requiring a trained investigator.

The other big problem with IR cameras is that they are limited in range by the IR light source used. Most only have an IR LED mounted on the camera. This can limit the range to as little as 30 feet. Additional IR lights can be installed, away from the camera, increasing the range. Always test an IR camera installation to ensure that there is adequate IR lighting in the area where the image needs to be captured.

Fixed vs. Panning Cameras

Many people like panning cameras, more for the fact that they are providing a changing scene, rather than a constant, still image. However, any criminal can time the pan of the camera and find a "window" to slip through. For this reason, panning cameras should only be used in conjunction with other fixed cameras. In such a case, the criminal may pay so much attention to the panning camera that they ignore the fixed one.

Panning cameras are the most useful for keeping a general eye on a large area, looking for potential problems. However, for gathering evidence of a crime, fixed cameras are better.

Digital vs. Analog Cameras

Originally, all security cameras were analog; however, today, many are digital. The video signal is digitized in the camera, and then transmitted to the control/recording center in a digital form. This allows the use of Cat -5/Cat-6 cables (Ethernet cables), which are much less expensive to buy than the coaxial cables needed for analog cameras.


Proper lens selection is probably the most critical aspect of camera selection. The first issue is whether to use a lens with a manual iris or one with an automatic iris. The iris controls the amount of light entering the camera. In cases where this is a constant, such as in the reception area of an office, a manual iris is best. Then it can be set for maximum visibility and left that way. In cases where the camera is subject to changes in light level, such as outdoors, an automatic iris is best.

The other major issue involving lenses is the focal length. This determines the camera's viewing angle. As previously mentioned, it is important not to waste the camera by taking pictures of empty walls. Proper lens selection provides the ability to surveil the necessary area and no more.

Focal Length

Viewing Angle Width

Viewing Angle Height

Field of View at 10 feet

Field of View at 25 feet

Field of View at 50 feet

3.6 mm



15 ft.

38 ft.

75 ft.

4.0 mm



12 ft.

30 ft.

30 ft.

4.3 mm



11 ft.

28 ft.

58 ft.

6 mm



8 ft.

19 ft.

38 ft.

8 mm



6 ft.

14 ft.

29 ft.

12 mm



4 ft.

10 ft.

19 ft.

16 mm



3 ft.

7 ft.

14 ft.

60 mm

1 ft.

2 ft.

4 ft.

The field of view mentioned in the above chart is only the width. As security cameras still use a 4:3 aspect ratio, which means that the image height will be 75 percent of the width.

To determine if a specific camera and lens arrangement will work to surveil a particular area, it is best to lay out the camera's location and the viewing angle on a floor plan of the building, showing exactly how wide an angle will be covered. This should be done for both the width and the height.

Buying Security Cameras on eBay

There is an extensive selection of security cameras regularly available on eBay. Many of these are from eBay companies that specialize in home security. These sellers are able to answer your questions about the products they sell and about installing a video security system in your home or small business.

To find security cameras on eBay, start by selecting Electronics from the main navigation menu on the eBay home page. From the main "Electronics" page, select TV , Audio & Surveillance. On that page, select Home Surveillance from the navigation menu. Finally, select the category Security Cameras.

There are filters located on the security camera page that allow you to further refine the search by camera type, connection type, and condition. Used cameras often work just as well as new ones, although they may be slightly larger.


Properly selecting security cameras for a home, office, or small business is largely an exercise in determining what needs to be watched. There is always a tradeoff between having enough cameras to properly surveil everything and the cost of the system. When in doubt, it is best to provide extra cameras, as this is an investment in security.

The two priorities in any video surveillance system are to capture any criminal act on video and to be able to identify the perpetrator of that crime. Camera placement and lens selection is very important to ensure that these two goals are properly attained. In many cases, police agencies are unable to accomplish anything with video surveillance footage, as it does not show enough detail. Close-ups that show faces are needed for proper identification.

Selecting the right camera and lens for any particular location is of extreme importance. Ideally, the lens should only show what needs to be shown, without wasting video space showing empty walls. At the same time, using a lens with too small a viewing angle can provide too much opportunity for a perpetrator to slip through without being caught on video.

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