With known danger detectors the temperature sensor, typically an NTC resistor, is typically attached to the detector vertex, in order to detect the ambient temperature of the danger detector itself as independently of direction as possible. 
A serious problem in such detectors is also that the ambient temperature is only detected in point form by means of the NTC resistor.  This requires a very precise mechanical positioning.  Investigations in this area have shown that even deviations of less than 1 mm from the vertex point, meaning from the geometrically central position, can lead to significant directional dependencies.  In addition it is disadvantageously necessary for the NTC resistor to be mechanically protected from the environment, e.g. by means of a separate dome or a cover. 
A further problem is that the electrical connection of the NTC resistor to a corresponding evaluation unit, which is located on a circuit carrier of the danger detector, is made through a connecting line, which mostly leads through the optically-sensitive space of the alarm housing and through the measurement chamber for smoke detection located therein to the evaluation unit.  This leads to complex constructions in respect of the measuring chamber and makes the installation of the danger detector more difficult.  In addition optical scattering at the pass-through of the connecting line is disadvantageously possible. 
Disposing two or more temperature sensors, e.g., opposite one another, on the outer circumference of the danger detector is also known.  However disadvantageously additional components are necessary.  Also the additional effort for the installation and the electronic measurement evaluation is immense.