If you see an ad pop up on your phone shortly after you've had a verbal conversation about the same item, you might suspect that your phone is listening in to your conversation.
Although location services, browsing history, and cookies are much more effective ways that advertisers can keep track of us, there are some settings you can enable on your devices to reassure yourself that the apps on your phone have only the permissions you have set.
Cookies are saved on your smartphone just as they are on your PC. If you are worried about cookies from one browsing session being read by some of your other apps, you can use a browser such as DuckDuckGo.
This browser lets you clear all tabs and data after each browsing session so you can guarantee that apps can't gain any extra information from you that you are unaware of.
If Chrome is your default browser on Android, there are a few settings you can check for your peace of mind. In Settings > Privacy you can enable Do Not Track to make sure your browsing journey is yours alone.
Clicking on Clear browsing data will ensure that your habits are not remembered by the browser. You can choose which browsing data such as browsing history, cookies, and site data you wish to keep -- and which to delete.
You can even select the time range you want to ensure that only the last week's worth of data is erased.
If you have an iPhone, you can deny permission on an app-by-app basis. Click Settings > Privacy > Microphone.
The list of apps that have requested access to the microphone will appear on the list so you can allow or deny access per app. Screenshot is from an iPhone 6S.
If you are concerned about apps having access to your location, you can switch location off for every app on your phone.
Be aware that many of your favorite apps might not work as intended.
You can view a list of each permission that you originally granted to each app when you installed it from the store.
You can drill-down and give specific apps permissions (or not) to use the microphone or other features that you choose.