Life detector device of the type used for personal identification that uses the evanescent field of the guided light (5) inside a waveguide that preserves the polarization and where this waveguide (8) is configured so that the interaction of the light with the biometric element provokes a change in the polarization of the light as it exits the fibre with respect to the polarization it has when it enters, which is detected by a photo-detector connected to the fibre (10,15) this change in polarization of the guided light is characteristic of the user that is being identified.
