In some implementations, an apparatus includes a first microprocessor, a digital infrared sensor operably coupled to the first microprocessor, an ambient temperature sensor operably coupled to the first microprocessor, a battery operably coupled to the first microprocessor, a multi-vital-sign finger cuff that is detachable and removable from the apparatus and that includes: a printed circuit board, a SpO2 subsystem that is operably coupled to the printed circuit board and that includes a photoplethysmogram sensor and that is operably coupled to the printed circuit board, the photoplethysmogram sensor includes one infrared detector that detects infrared energy at two different transmitted wavelengths, red and near infrared, and a micro dynamic light scattering sensor, the micro dynamic light scattering sensor includes two photo diode receivers and one laser transmitter.