SkyBell is a smart doorbell with a video camera, microphone, and speaker in it. It connects via Wi-Fi, and allows you to see, hear, and speak to visitors that are at the door no matter where you actually are. Even if the visitor doesn't ring the doorbell, SkyBell's motion sensor will still alert you that someone is there.
SkyBell is built to withstand various weather conditions, and can operate from -40 to 150 degrees Ferenheit. It doesn't require batteries, since it can connect directly to power. It can easily be installed in place of your current doorbell, and syncs to the corresponding smartphone app.
SkyBell's camera uses a wide-angle lens, and you can check the live feed from the camera at any time from the smartphone app. The camera has night vision as well. If you're unable to get to the door or check the app right away, SkyBell can record visits to the server for playback later. It also has a "silent" mode if you don't want to be disturbed.
SkyBell is $199, and has apps for both iOS and Android.