Home Breathalyzer False Negative

I have one of those home breathalyzer kits (an alcosense elite 3) and it’s been useful on a few occasions the next day when it’s told me I’m over the limit and therefore I’ve refrained from getting behind the wheel.

When searching for false reading info on the internet almost all of it is about false positives but I’m concerned that my unit is giving me the opposite.

Last night I had 6 bottles of lager (8.4 units) and 3/4 of a bottle of red wine (7.5 units) during the hours of 4pm and 12am. I tested myself this morning at 10am fully expecting a result over the limit and got the “LO” result – which means trace or zero alcohol on my breath.

The thing is I can feel I’ve still got alcohol in my system and the 16 units I had should take until 4pm to be out of my system by the traditional calculation of 1 hour per unit from when you stopped drinking.

I have no intention of driving today as I’ll trust my own feeling over any device, but does anybody know what might be causing this obvious false negative? TIA.