Silicon complementary metal oxide semiconductor (CMOS) technologies are arguably the most important asset in the world of electronics. Focal plane arrays (FPAs) are one of the driving forces in the revolution of low-cost, mass produced, compact, and high-resolution imaging devices. The importance of these imaging systems in the visible spectrum has highlighted the need of their implementation into other significant electromagnetic regions such as infrared (IR) and Terahertz (THz). The unique characteristics of THz waves make them ideal for a variety of important applications ranging from security and medical imaging, explosive and drug detection, and non-destructive quality control testing. These applications are possible due to the non-ionizing nature of THz radiation, its transparency to many non-conductive materials, and distinctive spectroscopic fingerprints of a vast number of substances.<p> </p> Current THz imaging systems are usually restricted to laboratory use due the lack of compact, portable and roomtemperature operated sources and detectors. Therefore, the implementation of CMOS based THz detectors is key to promote the exploitation of low-cost, room-temperature, high-resolution, highly sensitive, and portable THz imaging systems. Here we present the monolithic integration of two types of THz FPAs fabricated in a standard 180 nm CMOS process. The imagers are composed of THz metamaterials (MM) absorbers coupled to a microbolometer, either vanadium oxide (VOx) or silicon pn diode, integrated with readout electronics to form 64 x 64 CMOS FPAs. The suitability of THz imagers for stand-off imaging of concealed objects was demonstrated in transmission mode by capturing images of metallic objects hidden in a manila envelope.