Most of the modern blood sugar testing machines require batteries and batteries eventually lose their charge. There are, of course, the battery-free urine strips which change color depending on bloodsugar level but they are not all that accurate.
Now, there is a push to see if tatoos can work, tatoos that change color depending on blood sugar levels. More will be posted regarding this new development. Its still at the experimental level so far as we know but if you would like to get further information on this potential way of determining bloodsugar, you might start by reviewing the video found in the following website: https://www.simplemost.com/tattoo-changes-colors-along-blood-sugar-levels/