For years, Amazon has been testing the limits of online deliveries — expanding the number of things you can order at the click of a button (sometimes literally), pushing shipments to arrive faster, toying with delivery by drones.

Now the company is pushing at a new boundary — the front door.

Amazon Key, a new service announced Wednesday, would allow couriers to open the doors of customers who opt in, in order to leave packages inside a house or apartment.

The service is only available to Amazon Prime members. It requires a smart lock, which can be unlocked remotely, as well as the Amazon Cloud Cam — a new Amazon security camera, also announced on Wednesday. Amazon Key promises to turn on the camera (pointed at your door) every time the door is unlocked and show you a video of the full delivery.

"Each time a delivery driver requests access to a customer's home, Amazon verifies that the correct driver is at the right address, at the intended time, through an encrypted authentication process," Amazon says in a statement. "Once this process is successfully completed, Amazon Cloud Cam starts recording and the door is then unlocked. No access codes or keys are ever provided to delivery drivers."

The service will also allow you to unlock the door for friends or family. Eventually, Amazon says, it will have options for service providers (like cleaning services or dog sitters) to enter as well.

A kit to start using the service, including a Cloud Cam and smart lock, begins at $249 and requires Amazon Prime membership ($99 annually). It's only available in certain cities (where Amazon handles deliveries directly).

Amazon Key addresses issues of security and convenience, while raising its own questions about security and privacy.

Using the service would prevent package theft and obviate the need to stay home or arrange for a spare key for a contractor or visitor.

But it requires customers to be comfortable with a smart lock controlled by Amazon andwith an Amazon-connected camera monitoring the inside of their home and communicating to the cloud. Even if users are willing to trust Amazon with that level of access to their homes, they might have other concerns; Internet-connected smart devices can be vulnerable to hacking.

Meanwhile, the unlocking of the front door might not be the key component of this new service.

The Verge points out that Amazon is on a "quest to manage your home life and integrate itself into your daily routine." The Amazon Cloud Cam is a direct challenge to smart-home cameras offered by Google's Nest, as well as Logitech and a host of other companies.

Offering a novel delivery service exclusively for customers who buy the camera might give Amazon an edge over the competition and put the camera in more homes.

Adding a camera that monitors front doors and is integrated with Alexa and the front lock "would be positioning Amazon to know a lot more about [people's] lives and habits, like when they leave the house in the morning, how often they go on vacation, and when they get back from work at night," the Verge writes.

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