My Mom lives by herself, and we visit or call an ask if she has taken her pills she will always answer yes. Then later on we will be putting away something or cleaning and find an entire set of her day's pills in odd places. Is there a "sugar pill" that will coat her tongue or mouth in a color to know she actually took them instead of saying yes and actually hiding them?
I know it's hard to get our parents to be honest in regards to taking their pills. I guess the only thing that helped me was being on the phone with her each time it was for "pill call". Even so, it's not fool proof but it got her to stop the ER visits until she moved to an ALF.
Otherwise, you have a great invention. Seriously, if you could make something or get someone to help you out with this that could detect the important meds on the tongue, then it really could help save lives even!
Try "pill call" maybe for now. Best of luck to you. I know it's hard.