Keepa is an app, which is extremely useful for online shopping on Amazon. The key feature of this app is that it kept price record of the amazon products. So, you can compare the current and previous prices and shop wisely. It also demonstrate price using price graph. It saves the time and money at the same time.
It also has a notification option. You can create your list and set notification price. When perticular product reach at that price point, you will get notification so, you can purchase it.