In order to be lawfully stopped by the police in New York, the officer must have had a reasonable suspicion, that the operator of the vehicle, violated a provision of the Vehicle in Traffic law, or the stop is an unconstitutional stop.
If the officer suspects that the driver has been operating the vehicle in an intoxicated state, the officer may request that the driver take a Preliminary Breath Test and Field Sobriety Tests. The Officer will use the result of these tests as probable cause to make an arrest for DWI.
The Preliminary Breath Test is typically performed by the driver blowing into a handheld breath alcohol tester. A Passive Alcohol Sensor (PAS) may also be used that can obtain a reading without a breath sample. These devices are used at the location of the motor vehicle stop, and are inadmissible in Court.
Field Sobriety Tests are tests used by police officers to determine if a driver is impaired by drugs or alcohol. Field Sobriety Tests may include the One Leg Stand Test, the Finger to Nose Test, the Walk and Turn Test, the Gaze Nystagmus Test, the Alphabet Test, the Rhomberg Test, or the Finger Count Test. Some of these tests require special training so officers generally do not use all of them at the time of the stop.
If the driver fails some of the Field Sobriety Tests and/or registers a high enough reading on the preliminary breath test, the driver may be arrested for driving while intoxicated (DWI) as there may be probable cause to make the arrest. The driver will then be taken to the station, and within two hours will be asked to take a chemical test with some sort of advanced infrared breath testing device back at the station. If the driver is unwilling to take the test at the station, he will be deemed to have "refused" the test. The driver may also choose to have a blood test.
Unless you have not been drinking at all, you may not want to take the preliminary tests as they may lead to the officer having probable cause to make the arrest. Even if you have not been drinking some people will fail some of the field sobriety tests even when sober. Keep in mind, that you are likely to be arrested anyway, if the officer thinks you are drunk, even if you are not, especially if the stop occurred late at night or very early in the morning.