Existing Global Navigation Satellite Systems offer no authentication of their satellite signals towards their civilian users. As a consequence, several types of GNSS-related attacks, including meaconing, may be performed and remain undetected. In the scope of the project “Developing a prototype of Localisation Assurance Service Provider”, which is funded by ESA and realised by the company itrust consulting and the University of Luxembourg, a methodology to visualise the beginnings and the ends of meaconing attacks by monitoring the clock bias of an attacked receiver over time was developed. This paper presents an algorithm that is based on this attack visualisation technique and is capable of detecting meaconing attacks automatically. Experiments in a controlled environment confirmed that the chosen methodology works properly. In one of these tests, for example, six meaconing attacks were simulated by using a GNSS signal repeater. The algorithm was able to detect the beginnings and the ends of all six attacks, while resulting in no more than two false positives, even though the average delay introduced by the meaconing stations (repeater) was just 80 nanoseconds.