Your phone knows a lot about you, but what about the phone companies behind the device?

They know even more.

Apple and Samsung are spying on your activity

Samsung and Apple phones have the right to monitor your activity using something called beacons (also called pixels) — which you may or may not realize is something you consented to by accessing and using the company’s services.

Both Samsung and Apple outline in their terms and conditions that they gather information on specific content from the web or your email while you use your phone.

The beacons are embedded in the content you look at while using your device, so every time you use your phone, you’re giving companies more information about you.

Read more: Could what your Amazon Alexa overhears be used against you?

Here’s part of Samsung’s user agreement about beacons:

“Beacons can be embedded in online content, videos and emails and allow a server to read certain types of information from your device, know when you have viewed particular content or a particular email message, determine the time and date on which you viewed the beacon and the IP address of your device.”

Beacons are used to more precisely market to you on your devices by building up profiles based on what kinds of things you do on your device. That’s often why advertisements for an online store or airline you just checked out pop up in your browser.

At this point, using these brands simply means consenting to this type of tracking, but at least knowing about it is a step toward safer use.

Read more: Millions of Android users vulnerable to new hacking threat

5 ways to keep your cell phone charged