Computer simulations become more and more an important tool in the field of automatic fire detection. An over all model of the automatic fire detection shall give the opportunity to simulated the process of fire detection including the fire, the fire sensor and the processing of the sensor signal. For the different parts of the over all model realisations exist. There are different types of fire models and models for fire sensors. But these are separate models. To allow the simulation of a fire sensor signal from the fire up to the response of the sensor the models have to be combined. One model to simulate fires is the Fire Dynamics Simulator (FDS) developed at the National Institute of Standards and Technology. This model is combined with a fire sensor model, that simulates the response of a fire sensor to a given fire situation, which is defined by the input parameters of the sensor model. For this combination an interface between the two models is build up. Inside this interface the output parameters of the fire model are converted to the necessary input parameters of the sensor model. In the first approach only smoke sensor are considered. For the simulation of the smoke development during a fire the fire model gives informations about the smoke mass density as results. The smoke sensor model needs informations about the size distribution of the smoke particles. So the different parameters have to be converted. Therefore mechanisms which influence the particle size distribution but not the smoke mass density have to be implemented in the interface. The combined fire and smoke-sensor model is verified by applying it to EN54 testfires and gives the possibility to simulate the response of different types of smoke sensors to a fire or a non-fire situation.