ᐅ Looking for a video door intercom system for a single-family home with two monitors for two floors.

If you want to have a video image, you need something to display it on. Of course, this can also be done using a smartphone or if a tablet is lying somewhere around. How practical that is, everyone can decide for themselves. The doorbell rings, and you run through the house looking for the tablet. That wouldn’t work for me. In that time, you might as well go directly to the door. Then you only need a button at the door and a chime inside. Also a solution, at the cost of a case of beer.

No, why not simply mount a display/monitor of this format on the wall? A tablet has many more functions and is likely more expensive (camera, sensors, GPS, Wi-Fi, etc.).

It is not suitable for this use. An intercom system is not like a DVD player where you simply connect a screen.

Yes, it probably really depends on the camera / video door intercom system.