How do electrical detectors work?

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I’ve seen how people use non contact voltage detectors to check whether or not a socket’s live wire has power. Non contact voltage detectors take advantage of capacitive coupling that occurs in AC in order to figure out if there is power or not.

Now, what people usually do is simply stick the detector into one side of the socket (the live side). This part completely confuses me, how is it possible to detect if there is power if the circuit is open? There is no connection from live to neutral which would close the circuit and allow current to flow.

Another thing that doesn’t make too much sense to me is that why does it only detect the live wire and not the neutral? When people insert the detector into the neutral side of the socket the detector doesn’t light up. The neutral wire is a must for current to flow, why doesn’t it also detect it?

Any help is greatly appreciated.

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