Explainer: How Do Voice Assistants Like Alexa and Siri Actually Work?

They sit in our kitchens, our pockets, and our cars, waiting patiently for a command. We ask Alexa for the weather, tell Siri to set a timer, or have Google Assistant add milk to our shopping list. It feels like magic—a simple, conversational AI ready to do our bidding.

But what actually happens in the few seconds between you saying “Hey Siri” and your phone responding? It’s not magic; it’s a lightning-fast, four-step journey that involves your local device, a powerful AI in the cloud, and some incredible feats of engineering.

Let’s break down how voice assistants actually work.

Step 1: The Wake Word – The Device is Always Listening (Sort Of)

Your smart speaker or phone is always listening, but not in the creepy way you might think. It’s not recording everything you say. Instead, it’s using a tiny, ultra-low-power processor to listen for one specific thing: the “wake word” (like “Alexa,” “Hey Siri,” or “Okay Google”).

The device uses a simple pattern-matching algorithm to constantly compare the sounds it hears to the wake word. It’s a passive process that uses very little energy and doesn’t store anything it hears. Only when it detects a match does the device “wake up,” start recording, and proceed to the next step.

Step 2: The Journey to the Cloud – Your Voice Takes Flight

Once you’ve spoken your command (e.g., “…what’s the weather like in New York?”), the device records that small snippet of audio. The device itself isn’t smart enough to understand the complex meaning of your sentence. So, it compresses that audio file and sends it securely over the internet to a massive data center—this is “the cloud.”

• The Technology: This process is called Speech-to-Text (STT). On the server, a powerful AI model transcribes the sound waves of your voice into digital text. It converts your spoken words into a sentence that a computer can read: "what's the weather like in new york"

Step 3: The AI Brain – Understanding Your Intent

Now that your command is in text form, it’s sent to the main AI brain. This is where the real “thinking” happens.

• The Technology: This is called Natural Language Processing (NLP) and Intent Recognition. The AI analyzes the text to figure out what you actually want. It breaks down the sentence:
  • It identifies the core intent: “weather.”
  • It identifies the key entities: “New York.”
  • It understands this is a question, not a command to play music or set a timer.

Once the AI understands your intent, it queries the relevant information source. In this case, it pings a weather service API for the latest forecast in New York City.

Step 4: The Response – Turning Text Back into Speech

The AI now has the answer in text form: "The weather in New York is 75 degrees and sunny." But it needs to deliver that information back to you in a natural, conversational way.

• The Technology: This is Text-to-Speech (TTS) synthesis. A different AI model takes that text and converts it back into a human-sounding audio file. Over the years, this technology has evolved from robotic, choppy speech to the smooth, nuanced voices we hear today.
• The Final Journey: This new audio file is then sent from the cloud server back to your device, which plays it through its speaker.

All of this—from the wake word to the spoken response—happens in the blink of an eye, typically in less than a second. It’s a breathtakingly complex journey that combines on-device hardware, high-speed networking, and multiple layers of sophisticated AI to create an experience that feels as simple and natural as talking to a person.