Replacement or deterioration of seismic instruments and the evolution of the installation conditions and sites can alter the seismic signal in very subtle ways, so it is notoriously difficult to monitor the signal quality of permanent seismic stations. We present a simple tool, energy ratios between each pair of the three recorded components, aimed at characterizing and monitoring signal quality, as a complement to existing methods. To calculate stable daily energy ratios over a large frequency range (0.01 Hz – 5 Hz), we use the daily median energy ratio over all 5-minute windows within the day. The method is applied to all GEOSCOPE stations, for continuous BH channel data collected since 2001. We show applications to identify past gain problems (stations ROCAM and CRZF), to provide feedback after field interventions at remote sites (Antarctic station DRV), and to shed light on complex instrument problems (stations ECH and KIP). Our results show that component energy ratios have excellent time resolution and that they are visually simple for identification of problems. They can be used both for ongoing continuous monitoring of the signal quality, or as a tool to identify past problems. The associated python codes are available on GitHub.