How many cameras
do I need?

A detached house usually needs two or three cameras: the front door, the garden or garage entrance, and one covering the back if it can be reached from outside without climbing a wall. An ordinary flat can be covered with a single camera at the front door, unless it has a terrace or patio with its own access, which adds a second. Adding cameras for a feeling of security doesn't help: if two point at the same stretch of inside corridor that nobody is going to enter from outside, one of them is surplus. The question that really decides the number isn't how many square metres the house has, but how many different points there are through which someone could get in without forcing anything. Count those points first, group the ones that can be seen from the same spot, and the number almost always works itself out below what you imagined before looking at it calmly.

Three to four cameras for a small shop: the door, the till framing the hands rather than the customer's face, the stockroom or back room, and the aisle with the most valuable goods. In long, narrow premises or ones with several blind spots, it is worth adding one for each change in line of sight, because a long aisle seen from a single point leaves the ends blurred or out of frame. A common mistake is putting two cameras on the same display area and none on the back room, which is usually where something actually happens, if it happens at all. Before deciding the number, walk round the shop thinking about which three things you would need to prove if something happened one day: who came in, what they took and where they took it from. Those three answers almost always tell you which cameras you need; everything else is optional.

Two ordinary ones, well placed, almost always, and for a simple reason: the usual problem with an installation isn't image quality, it is that the incident happened exactly where no camera was pointing. A single high-end wide-angle camera doesn't replace two covering different angles, because a very wide lens distorts the edges and loses useful detail exactly where it is needed most, in the corners of the frame. Putting your whole budget into one good camera only makes sense when there is a single point that really matters and no budget for more: for example, the till of a very small business with no other genuine critical point. Outside that specific case, spreading coverage across two points almost always beats putting all the quality into one.

Multiply each camera's bit rate by the hours it records each day and the number of days you want to keep footage. A camera set to 4 Mb/s recording non-stop generates around 43 GB a day, so four cameras keeping a full month need roughly 5 TB. Recording only when there is motion brings real usage down considerably, but it is worth sizing the drive for the worst day of the month, not a quiet one, because a drive that runs out two days before the month ends is useless. Two things push usage up without you noticing: cameras pointing at areas with leaves, rain or lights that flicker at night, which force the sensor to encode more information because of image noise. Always check actual usage with your cameras in place, not with the manufacturer's spec sheet.

One month at most. After that, footage has to be deleted, unless it records a specific incident that is going to be handed to the police or a court, in which case that particular recording is kept, not the whole month's archive. In practice this means the recorder has to be set to overwrite in a loop rather than accumulate indefinitely, which is exactly the opposite of what many people think gives more security. Keeping footage longer than necessary adds no protection, because almost no incident takes weeks to be noticed and reported; what it does add is a retention obligation you have to be able to justify if anyone asks. Decide first whether a week is enough, which covers almost any ordinary incident, or whether your particular business needs the full month, before sizing the drive.

Only at the minimum strip needed to cover your own entrance, whether that is the door, the gate or the garage entrance. Recording the whole pavement, the road or the front of the house opposite isn't allowed for a private individual or a shop, because the governing principle is that you may only capture what is strictly necessary for your own security, not monitor the public highway in general. In practice it is easy to check: if, when reviewing the frame, you can see more street than you need to know who is at your door, narrow the angle or reposition the camera. This doesn't reduce the camera's real usefulness, because the value lies precisely in that narrow strip in front of your entrance, not in a panoramic view of the whole street.

It depends on what you want to be able to prove afterwards. The door camera tells you someone came in and at what time, but not what they did inside or what they took; only a well-placed indoor camera tells you that. If the premises have goods on display, a till or a stockroom with valuable stock, the indoor camera is the one that provides genuinely useful evidence on the day it is needed, while the door camera serves as confirmation of when they came in. In a home the reasoning barely changes: if there is nothing inside you might need to prove beyond the fact that someone got in, the outdoor camera may be enough. The practical rule is to ask yourself what you would need to show if you had to explain what happened tomorrow, and put the camera where that answer lies.

Yes, as long as the recorder and cabling are sized with that in mind from the first installation. It is the decision people regret most afterwards: a recorder bought with exactly enough channels for today's cameras has to be replaced entirely on the day you want to add just one more, because recorders don't take extra channels once installed. Leaving one or two channels free and an empty conduit run to the points where you might one day want a camera costs very little during the initial installation, and saves a whole job of building work later. The same goes for the drive: if you buy it just big enough for what you record today, adding cameras later means replacing it too. Designing the installation for two or three more cameras than you need right now is the cheapest way to avoid doing the work twice.