Snickometer

Snickometer, commonly known as Snicko, is a system used in cricket to determine whether the ball edged[a] the bat, for a potential dismissal such as a catch or leg before wicket.

It does this by showing a frame-by-frame replay of the footage of the ball passing the bat alongside a waveform displaying the soundwave of an oscilloscope connected to a sensitive microphone near the stumps.

[1] The newer version currently in use is called Real Time Snickometer (RTS) and does not need to be manually synchronized for every piece of footage, making the process much faster.

[6] When the Decision Review System (DRS) was introduced to test cricket, initially Snicko was not considered accurate enough, and so another edge detecting tool Hot Spot was used.

It is easier to tell where the ball contacted precisely with Hot Spot, but that system has the disadvantage of needing a clear angle, which is sometimes obstructed by a fielder or umpire.