Siri, watch out: personalized search service Google Now is coming to iOS

Google(s GOOG) already has some really compelling apps that are meant to replace core services on the iPhone: apps like Gmail, Drive, Google Maps, Chrome, Capture and others. Now with an update to the Google Search app for iOS(s AAPL), the company has effectively trained its sights on Siri by adding Google Now to iOS.

Google Now iOSGoogle Now has been an integrated feature of Android 4.1 since June 2012, but starting Monday, it will, for the first time, be available on the iOS platform. (And no, Google did not have any problem getting the app approved, company representatives said.) The service, which draws on a wealth of user information in Google’s mobile apps and desktop services, aims to give users relevant answers to questions before they’ve even asked them. That information pops up on a “card” on the screen.

For example: if you’ve entered your work address, every morning when you get up Google Now will check the traffic; if it’s going to be a slow commute, the card will pop up in the Google Search app alerting the user to leave earlier than usual for work.

Users can choose what kinds of cards they want to receive. If you want to receive notifications about package deliveries, flight delays, football scores or sightseeing suggestions, that can be set in preferences. Google Now will know when you get, for example, a FedEx delivery notification in your Gmail, and it can alert you to that. Or, it can know when you have an upcoming flight, also based on airline confirmation emails as well.

Using Google Now is equivalent to the “signed-in” experience of using Google services in the browser: it can share information across other Google services to help you and give you information it thinks you want. If that creeps you out — if you don’t want Google knowing where you work or where you’re going on your next trip — you can turn any of those services off. Google Now will still work, it just won’t be as “rich” of an experience, Tamar Yehoshua, director of product management at Google, told me.

There are lots of small differences — and one big, major difference — between Google Search with Google Now on iOS and Siri. Both are described by their creators as the mobile, digital equivalents of “personal assistants,” but Siri is the kind that you have to keep asking to complete tasks. Google Now is the assistant that, when given access to a lot of your crucial personal information, can preemptively do things for you before you ask.

Google said a version of Google Now for iOS is one of its most requested features. And based on the praise the Android version has received over the last few months, it’s very likely to be a big hit for Google.

For Apple, this brings the benefit of offering a useful and popular service through its App Store. But, looked at another way, this is yet another way that its main rival in the mobile world is able to deepen its relationship with its own customers on Apple’s platform. And that’s got to be more than a little bit concerning to the folks in Cupertino as the two companies do battle for the future of mobile technology.

Still, Siri does maintain a nice home-field advantage: it’s actually built into the iPhone’s operating system and can be accessed with a quick long press of the home button. Google Now, for all of its features, still has to be searched for or accessed through push notifications just like any other app.