Wi-Fi or wired camera: which to choose

A Wi-Fi camera looks simpler: no cable to run. But that convenience has a price, and it is better to know it in advance.

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Comparison

Five things worth knowing

Power is almost always neededWi-Fi carries only the picture. Most cameras still need a socket or a power wire. Battery models exist, but the battery has to be recharged regularly.
The signal depends on wallsConcrete walls, metal and distance from the router weaken Wi-Fi. The picture may freeze and break up.
Many cameras load the networkOne or two cameras run fine over Wi-Fi. Ten can already get in the way of other devices.
A wire is steadierA cabled camera does not depend on the router or neighbouring networks and can be powered over the same cable.
When Wi-Fi makes senseOne or two cameras in a flat, or where a cable cannot be laid or you would rather not spoil the finish.

Questions

Which is more reliable?

A wired system. It is the usual choice for a shop, an office or a warehouse.

Can they be mixed?

Yes. The main cameras go on cable, and a Wi-Fi camera is added at a hard-to-reach point.

Will a Wi-Fi camera record if the router hangs?

If the camera has a memory card, recording to it continues. Recording to the recorder stops until the link returns.