11 Blocks, but can be reduced to 8
This app let's you pick a relative location, a contact and a message to send, and it'll send that message once you arrive in your selected location.
I personally use it to let friends know that I made it back home safe after a long night, or just to give updated ETAs when on a long drive to a friend's house.
As an example, I live 45 minutes away from all my friends, so I'll set this up to go off when I'm about 10 minutes away and the message will say "Hey guys, I'm about 10 minutes out."
I just wrote this and my above examples are intended uses, this has not been field tested yet.