A device is disclosed for sensing a fluid, such as in a ventilation duct. In at least one embodiment, the device includes a sensing element, a housing accommodating the sensing element, and a supply duct and a discharge duct, which ducts at one end commucicate with the housing and which ducts at the other end communicate with an object that is to be sensed. In at least one embodiment, the housing is formed with a first passage portion for the fluid that is to be sensed; that the sensing element is positioned in the first passage portion; and that the supply duct opens into said first passage portion and that the discharge duct is connected to a discharge opening formed in the first passage portion and positioned at a considerable peripheral distance from the mouth of said supply duct in the first passage portion, so that the fluid that is to be sensed is actively made to pass the sensing element.