Google Pixel phones and Home speaker take on Siri and Echo

Google has placed a virtual assistant at the heart of its latest smartphones and first voice-activated speaker.

The two Pixel handsets are the first mobiles to trigger Google Assistant by pressing their home buttons, somewhat like Apple's Siri.

The Home speaker lets the same artificial intelligence tool be controlled without use of a touchscreen. It rivals Amazon's Echo.

Google also unveiled new virtual reality kit and a 4K media streamer.

Google's chief executive Sundar Pichai said we are heading towards an "AI-first world"

The Assistant has two key advantages over rival systems:

• it can hold a conversation, in which one question or command builds on the last, rather than dealing with each request in isolation

• it draws on Google's Knowledge Graph database, which links together information about more 70 billion facts, and has been in use for four years

However, the US company will have to overcome privacy concerns and convince users that chatting to a virtual assistant has advantages over using individual apps.

Google already offers the Assistant as part of its chat app Allo - but the software has been installed on only a small minority of phones that support it as yet.

Smarter phones

The decision to brand the phones with the Pixel name, rather than Nexus, marks a break with the past, and is intended to signify that they were designed in house rather than by another manufacturer.

The devices come in two sizes - with either a 5in (12.7cm) or 5.5in (14cm) OLED (organic light-emitting diode) screen - but otherwise have similar specs.

Google said the 12.3 megapixel rear camera they share was the best on the market - basing its claim on an independent test by DxO Labs. And as further enticement, it is offering unlimited storage for the photos.

Google said the Pixel phone has no "unsightly camera bump" - a nod to Apple's iPhone 7

Google also drew attention to the devices' glass-and-aluminium bodies, and specifically noted they featured a headphone jack - unlike Apple and Motorola's latest models.

Unlike most Android phones, the Pixel and Pixel XL will automatically install operating-system and security updates as soon as they are released.

But it is their ability to access Assistant as a standalone facility that makes them unique, at least for now.

"It goes one step further than tapping on the microphone in the Google Search app and getting a bunch of responses - it gives a conversational feel to what you are doing," Google executive Mario Queiroz told the BBC.

Google Assistant can suggest activities to its users

Users can, for example, ask for what films are playing at nearby cinemas, and then follow up the reply by saying: "We want to bring the kids," to narrow down the selection.

"Having a conversation - one where you ask a question and then follow-on questions - is a much more natural way to interact, and you would think that would offer a better user experience," said Brian Blau, from the consultancy Gartner.

"But we haven't had that type of system offered at the mass market level before, so it's hard to say how well it actually do."

The Pixel will start at £599 and the Pixel XL at £719 when they go on sale on 20 October.

Lighter VR

The Daydream View headset is a two-thirds of the weight of Samsung's rival Gear VR

A month later, Google will launch the Daydream View.

The virtual reality headset and motion-sensing controller make use of Pixel - and other forthcoming compatible phones - as a display.

A near-field communication (NFC) chip automatically puts the handset into VR mode when it is fitted inside.

But the main advantages the £69 package offers a user over the existing Google Cardboard headset is a strap to hold it to their head and its wave-and-click controller.

Home v Echo

Home can be controlled by voice alone, but its settings are controlled by a companion app

Google says it believes smart speakers are about to become a "huge" category.

But Home enters the market nearly two years behind Echo.

The wi-fi speaker is activated by the trigger words "OK Google", following which, owners can use it to:

• get answers to questions

• control internet-connected lights and other smart home products

• play music via Spotify, YouTube Music, Google Play Music and other services

• set timers and alarms, create shopping lists and get travel updates

Most of this can already be done on the Echo, which benefits from being able to tap into additional third-party products as well as Amazon's shopping services.

But Google highlighted that Home could link up to its Chromecast media-streaming dongles, including a new higher-resolution 4K model, in addition to TVs and speakers with built-in Cast support.

Google says it has sold more than 30 million Chromecasts to date

"It gives you an easy way to distribute music throughout your home," said Mr Queiroz.

"You can also say, 'Play videos of John Oliver on my TV.'

"And your TV will power up and launch YouTube and play the clips. You won't have to reach for a remote and press the microphone button."

He added that the Assistant would soon be able to control Netflix as well.

The $129 (£101) device is launching in the US only next month, but is due to come to the UK next year.

Unlike most Google services, it will not play ads of its own, at least for now.

The latest Chromecast dongle plays 4K high dynamic range (HDR) video streams

Privacy concerns

Some households might be concerned by the idea of Google gaining a further way to track their habits.

But Mr Blau was not convinced Echo offered a better prospect.

"While Amazon does not do advertising like Google, it does have a large base of affiliated businesses that get access to the information about what you do and buy," he said.

"Anyway, consumers say that they are concerned about privacy but in general they usually don't act on those concerns."

Analysis: Rory Cellan-Jones, Technology correspondent

Google says Home's design was inspired by wine glasses and candles

It might seem from today's announcements that Google is showing it can become a hardware company with the kind of control over the entire user experience that Apple enjoys.

In fact, the key message coming from Mountain View is about software - and in particular artificial intelligence.

Google believes that 17 years of collecting data about its users and the world, coupled with its growing expertise in machine learning, have given it a lead over rivals like Amazon, Apple and Microsoft.

Google Home can be used to control TVs

That AI capability is now being showcased in Assistant, the conversational helper which will be at the heart of its own devices - and those made by its partners.

But its Achilles' heel could be customer concerns about privacy. Google may be smarter about anticipating its users every desire - but many may be cautious about handing over even more data to a business which already knows so much about them.