New apartments and homes may have a video doorbell to allow you to screen callers, but my house is a two-level Victorian that lacks such modern adornments.
My first thought was video doorbells from eBay. You can acquire both the wired and wireless varieties, some with displays fixed to the wall and others with multiple tablets that can be moved around the home. Since my house is two levels, at least two display stations or tablets would be required, which was beginning to move the price north of AU$500 dollars, and cabling the wired systems might require an electrician, as well.Mounting the camera was relatively easy, and I was able to run the thin DC power cable through a front window rather than needing to drill masonry.
I'm setting up some old, superfluous XP laptops to provide an always-on view upstairs and downstairs, and I've installed the OCX on various PCs in the house, so a camera window is always available.
While the audio works well, it's generally low quality and the camera speaker is low volume. It's fine for relatively quiet areas, but it may be inaudible in noisy areas.
The software will handle up to nine cameras if you need a video surveillance system, but I was happy with the modest investment to provide a security camera at the front door.