Last winter I stepped out my front door and smelled gas and called NSTAR and they came out with a truck and detectors and the whole lot. They smelled it too, but the concentration wasn't high enough to call it an emergency, so they put me on a repair list. Two weeks later I come home to find the street in front of my house spray painted by DigSafe and a note on my door saying I need to be home the next day. They came, ran a liner in the pipe from the main to my house, connected it inside, and were gone. No more gas smell.
Then they came 2 months later to replace my meter (which they do every 7 years).
--Mike