The U.S. Supreme Court recently ruled that the police do not need a warrant to require a motorists to take a breath test for alcohol. However a warrant is required for a blood test because it is more intrusive. A motorist of course can refuse to take the breathalyzer but if you do your license will automatically be suspended. There is an urban legend that if you have been drinking and stopped by the police that you should refuse the test. To do so is usually very bad as it will result in an automatic suspension and usually the prosecutor will not consider any sort of reduced charge. My advice is that unless you have regrettably killed or injured someone you should comply and take the breathalyzer.
For those of you that find yourselves in a situation where you may have had a drink or two and having to drive, you might consider buying your own portable breath test and use it before you try to drive. You can buy them online for about a hundred bucks and keep it either with you or in your car. A good friend who owns a restaurant/bar and who because of the nature of his business occasionally has a drink or two, purchased one of these devices and routinely uses it before he will drive. If it is close to or over the limit, he will simply wait until he passes. A rough estimate is that an ounce of alcohol causes a .02 BAC. It takes the body roughly 1 hour to burn that .02.