The invention relates to a sensor device for capturing data when carrying out first aid measures for reanimating a person affected by a cardiac arrest. The sensor device is exactly positioned on the chest of the patient by means of a positioning-aid apparatus (5) and affixed by means of a fastening means (2). The thorax compressions, i.e., the pressing-in depth and compression frequency, are detectable by means of a motion sensor. A data-transfer interface allows communication, e.g. wireless communication, with a mobile terminal.
