How do virtual assistants like Siri and Alexa work, and how do they understand and respond to our questions?

Question

How do virtual assistants like Siri and Alexa work, and how do they understand and respond to our questions?

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Answer 1

They have a huge database of commands. The microphone lets it understand your voice (the same way voice typing does) and if what you say matches something in the database, they follow the command.
Most of them require your commands to be like 90% accurate or something, since different people speak differently, which is why they sometimes do something completely different from what you say.

To have them seem more like a person, they have a set of responses for when they don’t know what to do.