We detect terahertz radiation emitted by a blackbody object at room temperature. The probe consists of semiconductor detectors coupled to the cold finger of a compact cryo-cooler. The detectors are narrow conductive channels in two-dimensional electron gas, which is sensitive to variations of photon flux through the mechanism of excitation and rectification of plasma waves. The excitation has a resonant nature, with an unexpectedly narrow FWHM, below 10%. The key element of the concept is a compact cryo-platform, which enables us to use highly sensitive cryo-detectors, while keeping the system compact, ~34 cm side, and mobile. We discriminate the temperature variation of the blackbody object as small as 1.0 K at a distance of 1 m. There is room for further optimization of the detectors and optical systems to boost the temperature resolution down to 0.5 K and the operation distance to 5 m, which are needed for practical applications.