Particle detection can be done with many different sensors. In this case, the particle detector is based on avalanche photodiodes (APDs) integrated on standard CMOS technology. The integration of the sensors allows the possibility to integrate also the processing circuitry, reducing the volume of components, the complexity, and also the cost of the total device. The sensor is based on a double sensor detection to discriminate the inherent noise of APDs. An electrical model of the sensor, including noise modeling of dark counts and afterpulsing, based on fabricated component, has been developed to proof the suitability of the proposed detector circuit.