I visited the Palmer Earthquake Observatory once, years ago. They had racks full of expensive chart recorders, hooked to expensive, sensitive seismometers all around Alaska. With all that fancy equipment, everyone working there had on his desk a ``spring neck'' (aka ``bobblehead'') to tell them when there was an earthquake, or a heavy truck driving by.

These are little novelty items, a pair of flat plastic feet, a fat, weak spring body, and a plastic head which will wobble back and forth at the slightest breeze or disturbance. If you wanted an earthquake indicator, you could rig one of these so that if it wobbled very far, it would set off a battery operated buzzer.

I'm not sure why that would be worth while. If it's big enough to care about, I think you can count on it waking you up. My limited experience has been that earthquakes start slow, but build really fast. I can't imagine that 5 to 10 seconds is going to make much difference, particularly since anything sensitive enough to give that much warning is going to have lots of false alarms, and you won't run until you feel a real shake, even if you're awake.