Abstract: Apparatus for detecting alcohol on the breath including a microprocessor programmed to test breath temperature to guard against circumvention of the test. When the temperature test is passed, the breath alcohol concentration is measured. Responsive to the alcohol concentration, the microprocessor either: enables the ignition for a sober driver; enables the ignition for a tipsy but not drunk driver; disables the ignition, and imposes a programmed wait before allowing the test to be attempted again.