[en] An inertial and a uniformly accelerated harmonic oscillator are coupled to a scalar, massless field as models for particle detectors. The behavior of these detectors in several Minkowskian and Rindler quantum states and the back-reaction to the field are investigated. From the Bogolubov transformation between in- and outgoing particle states it is seen that neither the inertial nor the accelerated model gives rise to energy flux from the detector to the field or energy absorption from the field by the detector, although the accelerated one behaves as if it were immersed in a thermal state of the field. 15 refs., 5 figs., 1 tab