Devices, systems, and method are provided for tracking items in a store for processing a cashier-less purchase transaction. In one example, a method includes receiving sensor data regarding items associated with shelves of a store. The method also includes identifying a user entering the store. The identifying uses at least a device having wireless communication. The device has an application that is executed in associated with a user account of the user. Also, tracking the user movements while in the store. The tracked movements include detecting proximity of the user to a shelf having an item. And, detecting interaction data for the item on the shelf of the store by the user. The interaction data is configured to identify a type of said item and enable add said item to an electronic shopping cart of the user having said user account for enabling processing of said cashier-less purchase transaction. The method includes receiving data indicative of said user leaving an area of the store while the item is in the electronic shopping cart. Leaving is indicative that the user intends to purchase the item. An exit of the area includes one or more sensors for confirming that the user has left the area. The method includes processing an electronic charge to a payment service associated with the user account of the user for the item based on said confirming.