The term 'smart sensors' refers to sensors which contain both sensing and signal processing capabilities with objectives ranging from simple viewing to sophisticated remote sensing, surveillance, search/track, weapon guidance, robotics, perceptronics, and intelligence applications. In a broad sense, they include any sensor system covering the whole electromagnetic spectrum: this paper deals specifically with a new class of smart sensors in infrared spectral bands whose developments started some years ago, when it was recognized that the rapid advances of very large scale integration (VLSI) processor technology and mosaic infrared detector array technology could be combined to develop new generations of infrared smart sensor systems with much improved performances. Thus, sophisticated signal processing operations will be developed for these new systems by integrating microcomputers and other VLSI signal processors within or next to the sensor arrays, on the same focal plane, avoiding complex computing located far away from the sensors. Recently this approach has achieved higher goals by a new and revolutionary sensor concept which introduces inside the sensor some of the basic functions of living eyes, such as dynamic stare, dishomogeneity compensation, spatial and temporal filtering. New objectives and requirements of these new focal plane processors are presented for this type of new infrared smart sensor system. This paper concerns the processing techniques limited to the front end of the focal plane processing, namely, the enhancement of target-to-noise ratio by background clutter suppression and the improvement in target detection by a smart pattern correlation thresholding.