Now on Tap is a great Android feature coming very soon

Now on Tap, Google's wild new feature that, in essence, does Google searches inside apps automatically. It works like this: when you're in an app — any app — you hold down the home button. Android then figures out what is on the screen and does a Google Now search against it. A Now search is slightly different from your usual Google search, because it brings back cards that are full of structured data and actions, not just a list of links.

For example, in a tweet that mentiones Walter Isaacson. The Now on Tap card found him, and then you can say "OK Google" and ask a question that assumes Google knows what is on the screen, like "What books did he write?" It will then return a Google web search that answers your question.

It's a feature that infuses your entire phone with Google. It can search anything, anywhere, and it can connect you to other apps when you do it. Want to get from an email about dinner to having dinner? Hold down the home button, trust it to give you an OpenTable card for the restaurant mentioned in the email, tap it, and you've got a reservation. We've all gotten used to being able to be sloppy when we jam text into a Google search box. Now we don't even have to bother typing it out, we can just let Google read our screens for us.

If you're worried about the privacy implications of Google being able to read what you're doing in your apps, Google stated that you have to opt in to make the feature work and that nothing gets read until you initiate Now on Tap by either holding down the home button or saying "OK Google" inside an app.