The delivery wars ramped up Tuesday, as Walmart began delivering groceries right into their customers' refrigerators.

The InHome Delivery service, first announced by the world's largest retailer in June, will officially launch in Kansas City, Pittsburgh, and Vero Beach, Fla.

Walmart has said that more than 1 million shoppers will be able to use the new delivery option, which has Walmart employees select produce and other household items ordered by a customer online. They then deliver the items right into the shopper's kitchen or garage using smart technology that gives them a one-time code to enter.

The homeowner will be able to watch the delivery through their smartphone. The Walmart employee wears a camera that will livestream the delivery; if it doesn't turn on, the door at the customer's home won't unlock.

It's the latest move in the delivery tit for tat being waged by the nation's retailers, who are competing for customers by offering the most speed and convenience.

"InHome goes the extra step so that our customers can live their lives without worrying about making it to the store or being home to accept a delivery,'' Bart Stein, Walmart's senior vice president for membership and InHome, said in a blog post.

Subscriptions to the InHome delivery service will initially be $19.95 a month, though the first month will be complimentary.

Shoppers will have to make at least $30 worth of purchases each time, but they can order deliveries as often as they want.

The smart lock costs $49.95, but the installation will be free.

At a time when shoppers increasingly shop online and are finicky about the physical stores that they visit, retailers are trying to stand out by getting their products into the hands of shoppers more quickly than their rivals.

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Walgreens will become the first store in the nation to deliver purchases on-demand by drone when it kicks off a pilot program in Christiansburg, Va. this month.

And the delivery and pick up competition has been particularly fierce between Walmart and e-commerce giant Amazon.

Amazon has announced that it could begin using a self-driving drone to deliver orders within months, and the e-commerce giant began testing a delivery robot earlier this year. It has also set up lockers, where customers can retrieve items, at locations ranging from hotels to local banks.