How voice assistants like Siri and Alexa work

Listening for one word

A smart speaker or phone assistant is not sending everything you say to the internet. Instead, a small, low-power part of the device listens only for its wake word, such as "Alexa", "Hey Siri" or "Hey Google". This check happens on the device itself. Until it hears that word, it ignores everything else and keeps nothing.

When it thinks it hears the wake word, a light usually comes on, and it starts recording your request.

From your voice to an answer

1. Record: the device captures what you say after the wake word.
2. Turn speech into text: often in the cloud, sometimes on the device for simple requests.
3. Work out what you mean: AI decides whether you want the weather, a timer, a song or a smart light switched on.
4. Do it: the assistant fetches the answer or sends a command to another service.
5. Reply: it turns the answer back into speech and plays it.

Newer assistants use large language models, the same kind of AI behind chatbots, so they can handle more natural, back-and-forth conversation. See How chatbots work.

False wakes happen

Sometimes the device mishears something on TV or in conversation as its wake word and records a few seconds by mistake. Companies try to reduce this, but it is not perfect. That is one reason to check your history now and then and delete anything you do not want stored.

Privacy settings worth checking

• Review and delete recordings in the assistant's app. Many let you auto-delete after a set time.
• Turn off human review of recordings if the setting is offered.
• Use the mute button on smart speakers during private conversations. It physically disconnects or disables the microphones on most models.
• Turn on voice recognition so the assistant knows who is speaking, and limit what it will do for unrecognised voices, such as shopping.
• Require a PIN for purchases so children or visitors cannot order things by voice.

Tip: Do not connect door locks or alarms to a voice assistant unless you have set up a PIN or voice match. Someone shouting through a window should not be able to unlock your door.

Useful everyday features

• Timers, reminders and shopping lists.
• Hands-free calls, which can help older relatives or anyone with limited mobility.
• Controlling lights and heating with your voice.
• Reading out news, recipes and audiobooks.

Is it always listening?

In a sense, yes: the microphones are on so the device can hear its wake word. But listening for one word on the device is very different from recording and uploading everything. Independent researchers have tested popular smart speakers and generally found that they send audio after the wake word or a mishearing of it, not constant recordings. Still, if you are uncomfortable having microphones on in a bedroom or office, mute the device there or simply do not put one in that room. The choice is yours, and turning it off costs nothing.

Voice assistants are part of a wider smart home. Our analysis Are smart home devices safe? covers how to set them up sensibly.