If you are accessing it via the intent, as com.google.zxing.client.android.SCAN
it needs the Barcode Scanner application to be installed on the client. (Reference)
If it isn't installed, it redirects to the website and prompts the user to download. So strictly speaking, the user will have to be connected to the internet atleast once, in order to download the Barcode Scanner application (if he doesn't already have it)
Alternately
If you were to add a reference to the ZXing core library, into your project, you will be able to access it without having to direct the user out, to download Barcode Scanner.
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