A danger sensor (100) is described which features a first housing part (110), a second housing part (120), a detector unit (112) for detecting of a danger situation, wherein the detector unit (112) is arranged in or at the first housing part (110), and an electrical connection (114a, 114b) for connecting of at least one supply element (142a, 142b) which provides electric power to the detector unit (112) during operation. The first housing part (110) together with the second housing part (110) is designed so that a holding area is present between the two housing parts (110, 120) for the at least one supply element (142a, 142b), and that the volume of the holding area is variable by means of a volume adjustment element (130). Furthermore, an element (130) is described for adapting a danger sensor to different requirements regarding the power supply; also described is an arrangement for detecting of a danger situation and a method for retrofitting of the power supply to a danger sensor (100).