Sensor for measuring a vital parameter in the auditory canal of a person or animal, comprising: a sensor element attachment, which can be positioned at least partially in the auditory canal, a sensor element, which can be connected to the sensor element attachment and can be positioned at least partially in the auditory canal, and a positioning element, suitable for positioning the sensor element attachment in the auditory canal, wherein the positioning element can be connected at least at one end to the sensor element attachment, wherein the position of the sensor element in the auditory canal is determined by the depth of penetration of the sensor element attachment into the auditory canal, and wherein the positioning element has a suitable shape that follows the anatomy of the inside of the ear, and is suitable for pushing the sensor element attachment into the interior of the auditory canal in such a way that the sensor is held in a stable manner and a continuous measurement of the vital parameter takes place in the auditory canal, wherein the sensor element, the sensor element attachment and the positioning element are arranged at least partially in a housing and the housing can be adapted to the anatomy of at least part of the head of the person or animal, characterized in that the housing is configured to be at least partially elastic, wherein the housing is configured to be rotatable and size-adjustable, and wherein the housing comprises a piston and a guide, wherein the piston is at least partially aligned in the guide, wherein the piston ensures the size-adjustability, whereby the length of the positioning element can be adapted to any size, and wherein the piston and/or the guide comprise(s) a material comprising a plastic, a rubber, a silicone and/or an elastomer, and wherein the piston and the guide are size-adjustable in a 0° position, wherein the 0° position here is anatomically the forward or rearward direction as seen from the head of the person or animal, wherein a rotation of the piston relative to the guide by more than +120° or -120° is not possible, wherein a rotation out of the 0° position results in a deadlock, wherein in the deadlock a size-adjustability is not possible, wherein the deadlock of the piston and guide is provided by an elastic material and by a rigid material or by two rigid materials. a sensor element attachment, which can be positioned at least partially in the auditory canal, a sensor element, which can be connected to the sensor element attachment and can be positioned at least partially in the auditory canal, and a positioning element, suitable for positioning the sensor element attachment in the auditory canal, wherein the positioning element can be connected at least at one end to the sensor element attachment, wherein the position of the sensor element in the auditory canal is determined by the depth of penetration of the sensor element attachment into the auditory canal, and wherein the positioning element has a suitable shape that follows the anatomy of the inside of the ear, and is suitable for pushing the sensor element attachment into the interior of the auditory canal in such a way that the sensor is held in a stable manner and a continuous measurement of the vital parameter takes place in the auditory canal, wherein the sensor element, the sensor element attachment and the positioning element are arranged at least partially in a housing and the housing can be adapted to the anatomy of at least part of the head of the person or animal, characterized in that the housing is configured to be at least partially elastic, wherein the housing is configured to be rotatable and size-adjustable, and wherein the housing comprises a piston and a guide, wherein the piston is at least partially aligned in the guide, wherein the piston ensures the size-adjustability, whereby the length of the positioning element can be adapted to any size, and wherein the piston and/or the guide comprise(s) a material comprising a plastic, a rubber, a silicone and/or an elastomer, and wherein the piston and the guide are size-adjustable in a 0° position, wherein the 0° position here is anatomically the forward or rearward direction as seen from the head of the person or animal, wherein a rotation of the piston relative to the guide by more than +120° or -120° is not possible, wherein a rotation out of the 0° position results in a deadlock, wherein in the deadlock a size-adjustability is not possible, wherein the deadlock of the piston and guide is provided by an elastic material and by a rigid material or by two rigid materials.