What is a 'breathalyzer' used for in driving enforcement?

A breathalyzer is a device specifically designed to measure a person's blood alcohol concentration (BAC) through the analysis of breath samples. When law enforcement officers suspect that a driver may be intoxicated, they often administer a breathalyzer test to obtain a quantitative measurement of alcohol in the driver’s system. This is crucial for determining whether the driver's BAC exceeds the legal limit, which is essential for enforcing DUI (driving under the influence) laws.

The other options relate to different aspects of vehicle and driver safety but are not applicable to the purpose of a breathalyzer. Vehicle emissions are tested through separate mechanisms, response times are evaluated using different methods, and seat belt effectiveness is assessed through crash tests and safety ratings. Thus, the primary function of a breathalyzer remains singular, making it an essential tool in driving enforcement related to alcohol consumption.