Amazon said Tuesday that it had acquired Ring, a maker of internet-connected doorbells and cameras, pushing more deeply into the home security market.

The deal is worth around $1.1 billion, according to a person briefed on the deal who would speak only anonymously because the terms were private.

Ring is best known for a doorbell with a security camera inside. The device allows homeowners to monitor visitors at their front door through an app on their phone, even if they are not at home. Amazon has made home automation a major focus because of the success of its Echo family of products, which allow users to control thermostats, surveillance cameras and other connected devices using voice commands.

Amazon’s Echo Spot device already works with Ring doorbells, allowing people to look at footage from the cameras on the Echo Spot’s screen. Amazon had invested an undisclosed amount in Ring through its Alexa Fund, which finances startups that integrate their products with Alexa, the Amazon intelligent assistant that powers Echoes and other devices.

Buying Ring, though, suggests that Amazon has more ambitious plans for the product than it could achieve through a partnership.

Luke Schoenfelder, chief executive of Latch, a startup that makes a family of smart locks, said he believed that Amazon would make a more serious effort to enter the home security market and compete against companies like ADT, Comcast and Schoenfelder speculated that Amazon could seek to make home security part of its Prime membership service, which today includes free and fast delivery of orders and video streaming.

“You could imagine some kind of bundled offering with Ring’s capabilities,” he said.

ADT’s stock fell sharply after the deal became public Tuesday afternoon. It ended the day down 4.6 percent.

The companies declined to say much about their plans. “Ring’s home security products and services have delighted customers since day one,” Amazon said in a statement. “We’re excited to work with this talented team and help them in their mission to keep homes safe and secure.”

Ring’s statement said: “We’ll be able to achieve even more by partnering with an inventive, customer-centric company like Amazon. We look forward to being a part of the Amazon team as we work toward our vision for safer neighborhoods.”

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