Technology firms are “an existential threat” to humans, a former Google employee has warned.

Companies like Facebook are “steering” our thoughts through smartphones, according to Tristan Harris, who spent three years working as a Google design ethicist, before leaving in 2016.

He also believes their “goals” are fundamentally different to people’s.

11 useful Facebook features you didn't know existed Show all 11 1 /11 11 useful Facebook features you didn't know existed 11 useful Facebook features you didn't know existed Clean up your News Feed Most of us are Facebook friends with some people we don’t actually care about, and there are several ways to keep their updates off your News Feed. The easiest option is to head to the column on the left and open News Feed Preferences. From here, you can prioritise friends, unfollow friends, refollow friends you unfollowed in the past and even block specific apps. 11 useful Facebook features you didn't know existed Change ad preferences You can view a list of everything Facebook thinks you’re into and tinker with your ad preferences. A lot more information is displayed on the desktop site than the app, so we’d recommend doing this on a computer. Just open Settings and select Advert Preferences. 11 useful Facebook features you didn't know existed Manage notifications You can get notifications about pretty much anything on Facebook these days, and that can be seriously irritating. Choose what you do and don’t want to be notified about by going into the Settings menu and selecting Notifications. You might be surprised by the number of sections you have to trawl through. 11 useful Facebook features you didn't know existed Save data Facebook automatically plays videos in your News Feed, and that’s a problem if you aren’t on a generous data plan. You can change this by going to Videos in the Settings menu and disabling autoplay. On the app, there’s feature in the left-hand column called Data Saver, which also does this, but reduces the size of pictures too. 11 useful Facebook features you didn't know existed Reorder your News feed You can choose to order the updates that appear in your News Feed by time or importance. Just hit the three buttons next to News Feed Preferences on the Facebook site and choose between Top Stories and Recent Stories. 11 useful Facebook features you didn't know existed Download your data Facebook lets you download all of the immense amounts of data it has on you, including the posts you’ve shared, your messages and photos, ads you’ve clicked on and even the IP addresses that are logged when you log in or out of the site. It’s a lot of information, which you’ll want to get your hands on if you decide to quit the social network. 11 useful Facebook features you didn't know existed Find nearby places Nearby Places is actually a really handy tool, which lets you quickly find and research things like restaurants, hotels, museums and nightlife hotspots around you. It lives in the left-hand column, and also shows useful information like customer ratings, prices and distance. 11 useful Facebook features you didn't know existed Find free Wi-Fi Similarly, Find Wi-Fi is ideal for when you’re bored, running low on data or lost. It shows you all the places in your vicinity that offer free Wi-Fi, so you can head over and either relax or get some work done. 11 useful Facebook features you didn't know existed Save things for later Facebook’s ideal for killing time, but every now and again you’ll stumble across something you’re interested in right as you need to put your phone away. Fortunately, you can save posts for later by hitting the arrow in the top-right corner and selecting the Save option. Everything you save goes straight to the Saved section in the left-hand column. 11 useful Facebook features you didn't know existed Control tags When people tag you in posts or pictures, they don’t have to automatically appear on your profile. You can switch on Facebook’s Review Tags feature by going to Settings and Timeline and Tagging. 11 useful Facebook features you didn't know existed Delete your account To permanently delete your Facebook account, you need to head to Facebook’s Delete Account page. The site can take up to 90 days to process account deletion requests, but once your account's gone, it’s gone. You can deactivate your account instead, by going to Security and Login in the Settings menu.

“It's much bigger than addiction,” he told Evan Davis, during an interview on BBC Newsnight. “I'd actually call it an existential threat to the human race.”

According to Mr Harris, two billion people use a smartphone and two billion people use Facebook on a daily basis, and people check their mobiles over 150 times a day.

“In the 150 times a day when we check, what is going on in that moment right before we check? Is it because we’re sitting there and we make 150 conscious choices? That’s not what’s happening,” he continued.

“What’s happening is that we’re building up anxiety, as all the science shows, and as the anxiety builds it actually causes us to self-interrupt, and more research has shown that we actually interrupt ourselves about every 40 seconds.”

When asked to provide an example, Mr Harris referenced Snapchat’s Snapstreaks feature, which shows users how many days in a row they’ve sent a Snapchat picture to their friends. Snapstreaks end when 24 hours pass without a picture message being exchanged.

“We’ve hijacked what 100 million teenagers view as the currency of friendship,” he said. “The way kids know that they are or aren’t friends, is if that number shows that they’ve kept that streak up. That is where we’re developmentally harming an entire generation of children, undeniably.

“That's one of the clearest examples where it's not just addiction, it's the whole system. It’s going to get more and more persuasive too.”

What’s more, Mr Harris says that even if you know exactly how “persuasive technologies” work, they still have an enormous amount of power over you.

“The total surface area of how much technology is steering two billion people's thoughts is enormous, such that even when you're not looking at your phone, it's implementing or creating the kind of thoughts you're thinking about now,” he added.