Here is another WiFi doorbell that lets you see who is knocking on your door on your smartphone. The eRing Video Doorbell has 1080p resolution, 2-way audio, night vision, and motion detection. It sends you push alerts on activity to your iOS or Android device.
The camera doorbell supports 5 users monitoring it. It lets you record video to a SD card up to 128GB. Costs under $80 at this time.