How best to poll a sensor?

Use a timer:
Timer (Java 2 Platform SE v1.4.2)

Register a Java.util.Timer (above link) hat kicks off every 1 second and runs your sensor-checker-method().

Or if you have a main loop, do stuff, sleep, check sensor, loop. I think Loops are discouraged in event-driven programming whenever possible.

 

This feature should be built into the sensor service. Just like for the LocationManager where you can specify both an interval and a minimum change for the notification.