We have developed simple single pixel thermopile infrared (IR) detectors for monitoring clouds for the purpose of atmospheric research and for cloud detection over astronomical and astrophysical observatories. Those detectors were developed with 31 and 90, fields of view (FOV) and have a broad spectral response extended from 5.5 mu m to above 20 mu m centered on a wavelength of 10 mu m. This paper aims to give a detailed description of these detectors, and the methodology followed to construct and calibrate them. Results from observations with these detectors will be given. Simulations using MODTRAN software were carried out to examine the theoretical expectation of the measured IR sky temperatures by these detectors. Good agreements between the measured and simulated data were found. (C) 2009 Elsevier Ltd. All rights reserved.