The rapid emergence of the Internet of Things, machine vision, and artificial intelligence have imposed critical requirements on the miniaturization, energy efficiency, and cost-effectiveness of infrared detectors. To meet these requirements, new sensor technologies that can reduce the fabrication cost associated with semiconductor epitaxy and remove the stringent requirement for cryogenic cooling are under active investigation. In the technologically important spectral region of mid-wavelength infrared (3–5 µm), colloidal quantum dots are currently at the forefront of this endeavor, with wafer-scale monolithic integration and Auger suppression being the key material capabilities to minimize the sensor's size, weight, power consumption, and cost (SWaP-C). Infrared sensors based on colloidal quantum dots have been studied for decades, and harnessing the interband transition in these quantum-confined nanostructures has been the mainstream theme in optoelectronic research. More unique photophysical properties can be harnessed by utilizing the transitions within the conduction levels or valence levels, known as intraband (intersubband) transitions. In this presentation, we discuss the progress, challenges, and opportunities of MWIR sensors fabricated from Ag2Se intraband colloidal quantum dots, a heavy metal-free colloidal nanomaterial that has merits for wide-scale adoption in consumer and industrial sectors.