August's Doorbell Cam Pro is a hardwire-only smart buzzer. For $199, £155 or AU$265, you get live streaming, two-way talk and other key doorbell features. This model has free 24-hour video clip storage.
We haven't heard much about Blink's Video Doorbell since we saw it at CES. If you're already a Blink customer and have a Sync Module, the doorbell will set you back just $99 (roughly £75/AU$130). Otherwise, you'll have to spend $129 (about £95/AU$170) for both the doorbell and the module.
Amazon purchased security camera startup Blink in December 2017.
Nest's Hello offers HD live streaming and motion alerts, as well as Person Alerts and optional Familiar Face Alerts (with a Nest Aware subscription).
While Person Alerts notify you when the camera thinks it sees a person, Familiar Face Alerts will tell you who it sees if it recognizes the person from a saved database of friends, family and other folks who regularly visit your home.
The $199 (£155, AU$299) Ring Video Doorbell 2 is a very versatile device. Not only does it offer live streaming, two-way talk and other expected features. This 1080p HD buzzer can either be hardwired or rely on a removable, rechargeable battery.
It also works with Amazon Alexa, Google Assistant, IFTTT and Wink.
Ring's $249 (£195, AU$325) doorbell is a pricier DIY buzzer. But there's a big potential benefit -- this hardwire-only model is slimmer than most smart doorbells we've tested. That means it's way more likely to fit on that narrow doorframe where your existing wired buzzer is currently installed.