My understanding is a little shaky. Here it is. There are 3 ketone bodies you use as fuel. Acetone, Acetoacetate (AcAc), and BetaHydroxyButyrate (BHBA):
- Ketostix (pee sticks) measure AcAc leaving the body
- Ketonix and (other breathalyzers) measure Acetone in the body
- Blood monitors measure BHBA in the body (I think)
Over a few months a well adapted ketoer will pee less AcAc, effectively making the pee sticks meaningless. Most of their ketone bodies will now be the desirable and highly effective ketogenic fuel BHBA, and they won't be wasting a lot of ketones by excreting them in their urine (which is perhaps what's going on with you). At this point most peeps I know pass their ketostix onto a newbie.
So you need a more direct measure of what is actually happening in the body (not what is being excreted). That means, either breath or blood.
I'm not sure whether you can infer the BHBA levels from the Acetone levels but suffice to say that if you have a lot of Acetone in your breath / blood you are in ketosis. A lot of ketoers find it so obvious when their breath is funky that the whole measuring thing becomes moot. i.e. if your breath is funky you're in ketosis.
Ketonix is an effort to get a bit more refined than that. I dare say it's pretty primitive so far, but holds a lot of promise. You get three lights, low, medium, or high. The device gives you an estimate of your mmol of ketones (perhaps inferring BHBA from AcAc). The big problem is that the ketonix isn't at a price point that fits with the technology that's in it (IMHO). It's a breathalyzer, with a conversion matrix and 3 LEDS. I'm sure a lot of work has gone into developing it but I believe we can hack together the necessary data and breathalyzers for a fraction of the cost.
So, the short answer, is YES, a breathalyser would measure a different ketone. But more importantly it would measure it in your breath, which correlates more closely with the ketones in your blood.