As my very favorite Randall Munroe pointed out, and then saw real-life confirmation, Twitter can be used to give a few moments' warning when an earthquake comes.

If we can make a tree tweet about its feelings, I think we can rig sensors to tweet less abstract data. A tweet-a-quake could be as simple as:

5.9 in [NYC] 40.77, 73.98

I think that would be pretty obvious. As the wave progresses, it will trigger other sensors on its way, and you get more tweets.

You can even set your twitter client to auto-retweet tweets from the tweet-a-quake account, so you can focus on getting to safety right away.