A method and device for detecting and responding to impact loosening of thread joints at rock drilling, in which vibrations from a drill string (1) are sensed at the same time as a rock drilling machine (2) movable along a feed beam (6) exerts the drill string (1) to impacts without feeding the drill string (1) against a ground (3), the sensed vibrations are supplied to an analysis tool (4), the sensed vibrations are compared with known vibration patterns by the analysis tool, and a signal is sent to a control system (5) for controlling the rock drilling machine (2) for stopping an impact device of the rock drilling machine when the analysis tool detects that the sensed vibrations correspond to a known vibration pattern indicating that the thread joints have been loosened by impact.