I worked for a company that had licenses for Libre, Insulet and Dexcom and we had their serial APIs - but you had to plug it in to your computer, store the data

I worked for a company that had licenses for Libre, Insulet and Dexcom and we had their serial APIs - but you had to plug it in to your computer, store the data at our colo and use a Java applet to view it in the browser. In 2014. Unsurprisingly mobile apps have had more uptake since.