Sensing 120v AC motor running?

How can an arduino sense if a 120v AC motor is running? For instance, a sump pump with an internal float switch. I'd be happy if I could sense a rising or falling edge corrosponding to the motor starting or stopping. Or, I can poll to see if it's still running.

Ideally, I'd like something I could just plug the motor into that would in turn plug into the 120v mains.

I'm sure something like a sump pump would spike as it turns on and off, so I'm sure I'd need some kind of isolation.

Thanks for all your thoughts and advice. If I overlooked an answer to this already posted, please just point it out to me. I'm sure I'm not the first person to ask this type of question.

-Kevin

Try this Non-Invasive Current Sensor - 30A - SEN-11005 - SparkFun Electronics, or search more

Magician, thanks. I think this is what I was looking for. I didn't know what to call it. -Kevin