How many cameras do you need? The logic for homes, shops and warehouses

Do not start with square meters

The question we hear most is: how many cameras does a 200-square-meter shop need? This question cannot be answered honestly. Between the same 200 square meters being a flat hall with one door and being a store with two entrances, shelf aisles and a warehouse at the back, the number of cameras can double.

What determines the cameras is not the area but the likelihood of incidents. Where would a thief get in, where is the money kept, where do customers and employees meet, where do vehicles pull up? Every answer to these questions is a monitoring point. The number of cameras depends on how many of these points a single camera can see at the same time in enough detail.

Step 1: put the monitoring points on paper

Draw a rough sketch of the building. Mark the doors, windows, the safe, the warehouse door and the garden or parking entrance. Then write next to each point why it matters.

While making the list, look at the past too. If there was a burglary, a broken window or an argument between an employee and a customer before, the place where it happened goes at the top of the list. What has happened to neighboring businesses is also a good clue; on the same street, thieves often come in the same way.

This list is also useful when you ask for quotes. If you give the same list to the companies, you compare the quotes on the same need. Without a list, each company counts cameras by its own estimate and the quotes do not look alike.

• Every building entrance and exit: who came in, and at what time?
• Cash register and payment point: movement of money and receipts
• Valuable-goods shelves or the display window
• Warehouse door and goods receiving area
• Vehicle entrance and parking area
• Blind spots such as the rear facade, fire escape and roof access

Step 2: choose the detail needed for each point

A camera can see the door with a wide angle, but it cannot make out the face of a person 10 meters away. So ask this question for each point: do I only need to see movement here, or the face or the license plate?

At the entrance door, you need enough detail to identify a face. For this, the camera is placed close to the door, not too high above eye level, and with a narrow-angle lens. A camera looking at the whole parking lot sees movement and the number of vehicles with a wide angle, and does not identify anyone. Expecting two jobs from one camera is the most common mistake in quotes that show a low number.

These levels of detail are called detection, observation, recognition and identification in the international standard. It is called DORI for short, and a pixels-per-meter value is defined for each level. We covered the subject in a separate article.

Expert note: Do not place the door camera directly facing the door, with the light behind it. In daytime, light coming from outside darkens the face. Position the camera slightly to the side of the door, at an angle looking at it from inside.

Step 3: check the blind spots

After distributing the points to cameras, draw each camera's viewing cone on the sketch. The areas behind columns, shelves and trees show up. A thief often walks through these gaps.

A blind spot does not always require a new camera. Sometimes moving a camera two meters or changing its lens is enough. But if there is a facade that no camera sees, like the rear facade, at least one camera must be added there.

The camera distance calculation on our Tools page shows how wide an area the lens you choose will see at a given distance. You can use these values while drawing the sketch.

Think about the sketch once for night too. A corner that looks good in daytime may fall into the shadow of a street lamp at night. At points with poor lighting, either a camera with a long infrared range is chosen, or a motion-activated light is added at that point.

Example: three different buildings

In a detached house, the garden gate, front door, back garden and parking space are usually monitored. Two wide-angle cameras placed at the building corners scan the facades, and two cameras facing the doors get a close-up of whoever arrives. In many detached houses the plan stays between four and six cameras.

In a shop with a single entrance, the door, the cash register and the sales area are monitored separately; if there is a warehouse at the back, the warehouse door is added. If the shelves are high, as many cameras as there are aisles may be needed.

In a warehouse, loading ramps, forklift aisles, the perimeter fence and the office entrance are separate groups. As the number of ramps grows, the number of cameras grows too. In a warehouse with a high ceiling, the mounting height of the camera changes the image, so giving a number without measuring on site would not be right.

Common counting mistakes in quotes

If the number of cameras differs between two quotes, the reason is often that the need was interpreted differently. A quote with few cameras looks cheap, but it may not give you the footage you are looking for when an incident happens. A quote with many cameras is not always better either; having three cameras see the same area needlessly increases the recording and maintenance load.

When reading a quote, look next to each camera for which point it looks at and what detail it is supposed to give. If this information is missing, ask the company. A quote where the camera position is not clear cannot be compared.

• Covering the door and the parking lot with a single wide-angle camera
• Not taking into account a facade with no night lighting
• Placing the cash register camera on the ceiling at an angle that does not see the cash drawer
• Forgetting the back door and roof access
• Not thinking about obstacles that will block the view later, such as a tree, a sign or an awning
• Deciding the number of cameras by the recorder's channel count

Once the number is known: recording, disk and power

Once the number of cameras is settled, the recorder's channel count and the power budget of the PoE disk capacity and PoE switch (a switch that gives cameras both data and power over the same cable) are chosen accordingly. Do not buy the recorder with exactly the number of channels you need; you will want to add two or three cameras later. Disk capacity varies with the number of cameras, the resolution and how many days of footage will be kept. You can get a rough idea of this with the disk calculation on the Tools page.

Also think from the start about how long the recorder and the switch will keep running during a power outage. UPS calculation is also on the same page.

At Desa Bilişim, we make this sketch together with you during the site survey, and we write in the quote what each camera will see.

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