Chelsea were 2-0 up in first-half stoppage time against newly-promoted Hull on Jose Mourinho's return to English football when Hawk-Eye was deployed.
Branislav Ivanovic met Frank Lampard's corner with a firm header hit straight at Hull goalkeeper Allan McGregor, who saved on the line at the second attempt.
The referee's watch will only buzz when the ball crosses the goal-line, so it can be safe to assume Jonathan Moss felt no vibrations in a decision which is now out of his hands.
There were no protests from the Chelsea players and Mourinho and Hull counterpart Steve Bruce shared pleasantries as the half came to an end.
Replays also indicated the technology was working and Hawk-Eye's view of the incident was broadcast on television and on the big screen in the ground.
Chelsea midfielder Kevin de Bruyne was happy with how the system worked, telling Sky Sports 1: "It was clearly not over the line. The technology is good so there will be no questions further."