Ring makes doorbells that record live videos of customers' doorsteps, then sends the videos to their smartphones.

The doorbell could help Amazon customers trust its new service which lets couriers open people's front doors and put deliveries inside.

Amazon is reported to have paid more than $1bn to secure the Ring deal.

Amazon and Ring both declined to comment on the price, which was reported by Reuters.

An Amazon spokesman said it bought Ring to help customers keep their homes "safe and secure."

Ring said working with Amazon will allow it to "achieve even more" as it develops home security products.

Amazon's smart speaker Alexa already works with Ring gadgets and Amazon's venture capital arm invested in Ring last year.

Founded in 2012, Ring has more than 2,000 employees, about one million customers and estimated sales in 2016 of $155m, the Los Angeles Times reported last year.

The firm was previously known as Bot Home Automation.

Amazon already makes products for the home, such as its "Cloud Cam" security camera and voice-controlled devices like the Echo speaker, which users can command to perform tasks such as turning on and off lights and playing music.