An inappropriately chosen tactical procedure and means during a police intervention against highly dangerous subjects may lead to an escalation of the conflict and to further threats to the interveners and to the subject against whom the intervention is conducted. The main objective of this article is to analyse the effectiveness of the technical device Taser, which uses an electrical discharge to temporarily incapacitate a human subject, identify the main causes of failure of it, and its implications in practice at the incident level. The paper is based on the presentation of current scientific evidence in available electronic databases (Web of Science, Scopus; using keyword taser), and the data are compiled into a clear graphical form through the principles of the Fault Tree Analysis (FTA). A set of potential failure causes was identified from the human factor, the role of technology, and environmental influences. The taser was found to be a conditionally effective technological device with a wide and difficult to determine range of effectiveness depending on the method chosen. The findings have implications for training and education with a focus on minimising the risks of service intervention in terms of the effectiveness of this type of law enforcement agent.