A theoretical study is carried out in which a bare fiber optic cantilever beam, with no concentrated seismic mass, is proved to be suitable for measuring low‐frequency vibrations accurately. Its behavior was experimentally verified in the laboratory and can be approximated by a very simple transfer function that leads to straightforward signal processing. Some practical configurations, with accuracies as good as 0.5%, are given that depend on the operating frequency range. The simplicity of the architecture is highlighted. © 1996 Society of Photo−Optical Instrumentation Engineers.