As stated, "Ring" doorbell. $75 obo. Battery or hardwire, motion activated alerts, on demand video, 2-way talk, Wifi enabled with video like the one below.

Ring works with Amazon Echo. 

Also selling 3 Used Amazon Echo dots - 2nd Gen. $10 each obo.

We just switched over to Google Home and selling these. They're still pretty awesome for playing music, whole house audio, timers, weather, controlling a thermostat etc...

RING: