It has been noted that there is a new Google Now card that can remember products that you’ve searched for in the past, and when it detects that the item is on sale, it will then remind you of it. Sometimes we might forgot what we’ve searched for as it might not be too important so we could miss out on a sale now and then, but hopefully the new card will let more shoppers take advantage of the drop in prices.
Now while it might annoying that every product you’ve searched for will notify you, it seems that the reminder will only pop up if Google has detected that you’ve searched for it multiple times in the past which is probably a good indication that you’re seriously considering the product, otherwise why else would you bother, right?
Also presumably clicking on shopping links in search results will help Google identify that this is an item you’re interested in, versus searching for product reviews or looking for technical help on the product that you’ve purchased.