[wyred]

I would guess they have devices that detect light and sound. When the device detects a flash, it will start a timer and wait for the sound, which ends the timer.

Then based on the speed of sound, they can estimate the distance of the strike.

With many of these devices all over the place recording the data, using math, they can pinpoint the location of where the strike was.

[4mnt]

No sound, as it does not travel far enough and is easily disrupted by any other sounds in the area of the detector. I think it is just waiting for input of an electro-magnetical wave, then timestamps it and sends it to the server. The server can calculate the position with just the difference in arrival time to each station, and the position of those stations.

[anonymfus]

There is a project to detect lightnings over Moscow with cheap sound-only detectors on the roofs of skyscrapers, they managed to restore ever shapes of lightings in 3D with it:

http://habrahabr.ru/post/211701/ (description of their technology in Russian)

http://flashlook.ru/ (official site, no realtime translation now because of lack of funding, there are some prerecorded lightings)