The Digital PeepHole Viewer uses an LCD panel to display who is at your door without alerting them to your presence. Simply push the button to see a large image of the person outside your door. The viewer compensates for low-light images and eliminates “fish eye” distortion. Repeated presses toggle between regular and zoom modes.
It can also take an image of the visitor at the door, and keeps the image on a Micro SD card. You can buy accessories like a Motion Activated Sensor and a Knocking Sensor.
I sure could have used this in some of the apartments and houses I use to live in.