What was, until recently, a novelty piece of technology has become a potential multibillion-dollar opportunity for search giant Google and retail behemoth Amazon.
This year, Amazon paid US$1 billion ($1.47b) for Ring, a start-up that pioneered smart doorbells in the US.
Google, meanwhile, has launched Nest Hello, a rival video doorbell brand. The product comes from its Nest business best known for connected thermostats that Google bought for US$3.2b in 2014.
Suddenly, these tech companies want a piece of your front door.
"It was a market that was there but it was overlooked," says Jamie Siminoff, chief executive and founder of Ring.
"When Uber came out it showed how big something can get - that there is a totally different market if you change it. That's what Ring has done as it has expanded, delivering to people effective and affordable security."
Ring's £89 ($175) video doorbell emerged as one of the most successful pieces of hardware from the "internet of things" boom - the kinds of internet connected products such as smart fridges or thermostats.
The home security market is seen as ripe for expansion. Despite falling crime rates in many Western cities, the market is expected to grow from about US$31.6b in 2015 to US$57.73b in 2022, according to analysts Stratistics MRC.
The company rebranded from Doorbot to Ring. "We are building a ring of security around your home," says Siminoff.
Ring's device links to a user's smartphone, meaning that they can see who is ringing the doorbell wherever they are, through its app. Ring also sells smartphone connected home security cameras.
This year, Amazon made its move into the market, announcing it had bought Ring for $1b. "I think we were really lucky to attract them," Siminoff says.
But Amazon's ambition goes beyond simply securing the neighbourhood. With the purchase of Whole Foods and pharmaceutical delivery start-up PillPack, Ring represents a strategic play for Amazon to secure the last mile of deliveries from its retail business.
Last year, it launched Amazon Key. This somewhat terrifying technology includes a "smart lock", which can be unlocked with a smartphone by delivery couriers - complete strangers.
The couriers can then enter the home to drop off packages, even when no one is around.
Ring squares the circle for Amazon, giving them a camera at the front door and instant access to an entire network of Ring users.
The Nest Hello is a smaller, slimmer doorbell.
Users can give a specific code to, say, the cleaner, which works between the hours of 10am and 11am, before deactivating it.
This means contractors, cleaners, plumbers or dog walkers can come and go when nobody is in. According to Nest, the Hello camera is not about that "last mile" delivery, which is spurring Amazon. Instead, it acts as a way to offer a full service of smart home devices.
It adds to the convenience. Changing the way people think about their home security also hints to an economy where deliveries arrive at the home multiple times a day.
The doorbell can be seen as a soft entry point to the smart home. Not everyone immediately needs an Amazon Echo smart speaker, but doorbells are ubiquitous. Amazon and Google have taken to bundling their video doorbells with versions of the smart speakers to encourage adoption.
There are concerns about these products. Nest's camera comes with facial recognition. Is it ethical to keep tabs on the comings and goings of family members and children?
Perhaps crucially for both companies, Nest and Ring cameras both offer subscription-based services, tying consumers into their competing ecosystems.
"It is about creating a digital relationship with consumers," according to Thomas Husson, analyst at Forrester.
