If automation is the future of personal computing, we should all expect to see a slew of apps like the Pocket Doorbell app.
Here's how it works. Assuming you have your friend's addresses in your Contacts, the app will alert you when you are approaching a friend's house and give you the option of either calling or texting the friend to tell them that you are at their place.
Do you need an app like this? No, not really. But if removing the uneeded steps from everyday tasks—in this case, fishing through your Contacts for your friends information, though if you're going to their house, you will probably already have it readily available—then this is for you.
The Pocket Doorbell app is available now from the Apple App Store for $1.