“All Field Sobriety Tests are VOLUNTARY, NOBODY is ever required to take one. Nor is anybody required to blow in a hand held device in the field, it also is VOLUNTARY.”
Driving licenses in California are a privilege, not an absolute right. One condition is agreement to allow sobriety tests.
Refuse a test, lose your license. that simple.
Licenses can be revoked by the courts, by the licensing department or both.
In addition to alcohol, impairment can come via prescription drugs, cocaine, heroin, amphetamines, peyote, marijuana, etc.
I am not aware of the scientific research to prove the levels of impairment metrics, test procedures, etc.
Field Sobriety Tests are VOLUNTARY!!
A simple google search will help you understand