HotSpot is a television innovation - first seen during Channel Nine's coverage of the 2006-07 Ashes - that uses infrared camera technology to determine whether a batsman has made contact with a delivery, and if so, which part of his bat or body made contact.
Two powerful thermal-imaging cameras are positioned above the field of play, behind the bowler's arm at either end of a ground. These can remotely sense and measure the minute amount of heat generated by the impact of a cricket ball against another object. Computer technology then generates a negative image on which the point of contact is highlighted as a red friction "hot spot" for a second or two. HotSpot doesn't only record impacts between the ball and other objects, but also the bat hitting a pad or the ground.
Two hot spots would appear, one fractionally before the other, according to the sequence of the events. HotSpot is therefore useful in instances of bat-pad impacts in determining whether the ball hit bat or pad first.
HotSpot uses technology developed in the military for tank- and jet-fighter tracking. The technology was adapted for television by BBG Sports, the Australian company responsible for the Snickometer, in conjunction with Sky Sports. Channel Nine producer Steve Crawley described HotSpot as "100% backed up by science", as opposed to other applications.
HotSpot has only been used in cricket - though its services are not available to umpires under the current referral system - but work is underway to adapt the technology for use in tennis.