Hammacher Schlemmer has a personal thunderstorm detector.
The device detects cloud to ground activity up to 75 miles away, which is before you can see or hear the storm.
On storm detection the device flashes and displays a text message telling the impending storms ETA.
A 9 volt battery gives 90 hours of operation and they include a case and AC adapter.
However, at $430 I think I’d watch the weather channel on TV or track storms on my Blackberry. I know that if the clouds look omimous to expect a storm.
This is something that needs to be a lot cheaper (i.e sub $200) to really be attractive to the market.