I just tried the ketone strips in my Diet Pepsi, and my DH's Dr Pepper. There was no difference, although they both looked a little bit falsely dark because of the brown colour. Robin, are you sure your mom wasn't using the old Bayer DiaStix? Those measured both ketones and glucose. That's what I'd buy if I wanted to test restaurant drinks.

As for saliva ketone levels... I'm not sure that works. I'm pretty sure most of the "bad breath" ketones are being excreted out of your lungs, not your mouth. I would assume that there are too many confounders in your food, drink, and even mouthwash that could cause false positives. Even if you rinse the heck out of your mouth with water, well... you'd be washing away the ketones, too.