Apple posted a huge advertisement on the side of a hotel that overlooks the Las Vegas Convention Center, where rivals Google and Amazon are set to have a huge presence at this year's CES.

The message, which takes up about 13 floors of building, says : "What happens on your iPhone, stays on your iPhone" with the URL to Apple's privacy website.

While Apple's ad focuses specifically on phones, it's really a broader message about the companies it competes with in multiple industries.

Apple's message is clear: we're not trying to sell your data, while Amazon and Google use your data -- if sometimes anonymously -- to try to sell you stuff.

Amazon and Google are expected to have a lot to show at CES. Partners of both companies, from TV to appliance makers, will unveil gadgets with Amazon Alexa and Google Assistant built-in. Google has also said it tripled the size of its presence at CES from last year.

Apple might also be playing defense, though. Its HomePod isn't as popular as the Google Home or Amazon Echo. November data from research firm Canalys has Amazon and Google with 31.9 percent and 29.8 percent share of the smart speaker market, respectively, while Apple isn't even included as a big player.



Subscribe to CNBC on YouTube.