Now, using location data, Google Now will also let you know when items you have searched for in the past are available from nearby retailers or service providers.
Google uses the example of someone who searches for hiking boots, but has not actually gone to the store to pick some up. The next time that person is out shopping somewhere that happens to be near a store that sells the boots being searched, Google Now will throw out a card to let you know.
What we do not know is how long Google Now will remember the products, or if it limits how many items are actually tracked. The cards will provide the store location and the cost of the item. It is probably just a matter of time before we start getting information about whether or not the products we search are in stock or not.
source: Google+ via TNW