After visiting a Copenhagen safe injection site to interview staff regarding the methods used to keep intravenous drug users safe from disease and overdose, Nielsen became increasingly interested in finding a new and unique way to help ensure the safety of IDUs.
"Later, back in London, I continued my research by interviewing a number of heroin users and listened to their stories. Meeting these individuals fuelled my motivation to try and use design to lower the numbers of heroin related deaths in Denmark, UK and countries alike."
A pulse oximeter is a mobile and noninvasive instrument that can be used to effectively measure the oxygen saturation levels in a persons blood. Reflective pulse oximetry is the technology that makes it possible for this device to detect an overdose in Nielsen's design.
"An oximeter has a pair of small light-emitting diodes (LEDs) shining through a translucent part of the patients body, usually a fingertip. One LED is red, and the other is infrared. Absorption of these wavelengths differs significantly between oxygenated blood and deoxygenated blood. The photodiode on the opposite side of the LEDs measures how much red and infrared light has been transmitted to calculate the oxygen saturation. In some pulse oximeters, the LEDs and the measuring photodiode are on the same side and a reflective technology is used to bounce the light waves back to the same side of the device. Because blood circulates in momentary pulses, accurate measurements of oxygen levels adjust to the pulse rate, which is why pulse readings are also taken and displayed by a pulse oximeter."