This depends on the country. In mine (slovenia, a lot of drunk people here), you can not-sign the agreement with the breathalizer result, and the police will t

This depends on the country. In mine (slovenia, a lot of drunk people here), you can not-sign the agreement with the breathalizer result, and the police will take you to a clinic to do a blood test. Usually breathalizers show a bit less (larger tolerances/errors that the police have to subtract from the measured result), but if you're big/heavy enough, and the nearest clinic is far enough, it might be worth it, since you'll process some of the alcohol in the time to get the blood taken... depending of course if you're on the upper limit to a higher fine or near the lower limit.