Device to be used during chest compression in connection with CPR or for training, and more particular, a device for placement between the hands of a person performing CPR and the chest of a patient or manikin. The device is adapted to emit a sound when the chest compression is performed with a force that exceeds a predetermined value and optionally also emit a sound indication the intended frequency of the chest compression. Different mechanical and electronical embodiments are described, these includes an automatic switch that turns the electronic circuit on when the device is compressed and an embodiment having different predetermined forces depending on which side of the device is facing upwards.