Tired of standing in line? Wait a bit longer, and you may never have to again. Everyone from Amazon to Silicon Valley startups are trying to eliminate lines in retail stores. Amazon has opened 24 of its Amazon Go stores, which use cameras and artificial intelligence to see what you've taken off shelves and charge you as you walk out. Some startups such as San Francisco-based Grabango are closely mimicking Amazon's approach of using AI-powered cameras mounted in ceilings to identify what you've removed from a shelf and then charge you for those items. One of Caper's smart shopping carts. But others are trying an entirely different route to skipping the checkout: smart shopping carts. These companies have added cameras and sensors to the carts, and are using AI to tell what you've placed in them. A built-in scale weighs items, in case you have to pay by the pound for an item. Customers pay by entering a credit card, or by using Apple Pay or Google Pay. When a customer exits the store, a green light on the shopping cart indicates that their order is complete, and they're charged. If something goes wrong, the light turns red, and a store employee is summoned. One of Caper's smart shopping carts. The startups behind the smart carts, including Caper and Veeve, say it's much easier to add technology to the shopping cart than to an entire store.