The thinking is that sophisticated devices are needed for some biomarker studies and medicine. However, it is relatively simple to build some devices thought complicated with materials that are commonly available in electronic shops. For example, measurement of alcohol used to require sophisticated gas chromatography. With commonly available sensors, like a “MQ3 gas sensor” available for about $5, as you can see in the picture, numerous hobbyists have built alcohol breathalyzers. Thus, given the key sensor mechanism, it is relatively easy to build a device these days with electronic tools and gadgets available.
Given inexpensive sensors for various biology readouts, it would be great to build sensors for many diseases and even bad breath.
Look at the link below to see what has been done with the alcohol sensor, a phone and an Altoid box.