The 1-Wire lightning detectors are only available from Hobby Boards and take about 10 days to arrive, you can get some sensors in the UK from
Audon.
You'll also need the serial or USB adaptor to plug the detector into the PC.

I had an earlier version than is available now and that was good for the price.
If you have it near or on the house then it can be effected by light switches, florescent lights, electric fences or anything that creates a small electrical charge when it switches on or off. But you can tune these out to some extent.
Range wise, they are good for 25-30 miles (sometime more with a larger or higher antenna) but they only tell you that lightning is around, they don't tell you in which direction or how far away.
Hope that helps.