This study presents a novel, high-performance, non-invasive, self-powered InP/Pt/chitosan nanowire (NW) acetone sensor for monitoring breath acetone levels, which are directly correlated with blood ketones. The sensor exhibits an ultra-wide detection range from sub-ppb to >100,000 ppm at room temperature, covering the clinically relevant range from healthy individuals to those at high risk of diabetic ketoacidosis (DKA). The sensor's sensitivity and selectivity are enhanced by incorporating chitosan as a surface-functional layer and a Pt Schottky contact, enabling efficient charge transfer processes and a photovoltaic effect. The sensing mechanism involves an oxygen-facilitated two-step charge transfer process, leading to a redox reaction of acetone. The sensor has been integrated into a handheld breath testing prototype, the Ketowhistle, which successfully detects different ranges of acetone concentrations in simulated breath samples. This device shows great potential for non-invasive ketone monitoring, particularly for DKA prevention in people with diabetes.This study presents a novel, high-performance, non-invasive, self-powered InP/Pt/chitosan nanowire (NW) acetone sensor for monitoring breath acetone levels, which are directly correlated with blood ketones. The sensor exhibits an ultra-wide detection range from sub-ppb to >100,000 ppm at room temperature, covering the clinically relevant range from healthy individuals to those at high risk of diabetic ketoacidosis (DKA). The sensor's sensitivity and selectivity are enhanced by incorporating chitosan as a surface-functional layer and a Pt Schottky contact, enabling efficient charge transfer processes and a photovoltaic effect. The sensing mechanism involves an oxygen-facilitated two-step charge transfer process, leading to a redox reaction of acetone. The sensor has been integrated into a handheld breath testing prototype, the Ketowhistle, which successfully detects different ranges of acetone concentrations in simulated breath samples. This device shows great potential for non-invasive ketone monitoring, particularly for DKA prevention in people with diabetes.