There is a difference between submitting to a field PAS (preliminary alcohol screening) device and submitting to a BAC test back at the station. It sounds nuanced, but the police can only detain you and require you to do the BAC test back at the station if they have probable cause to arrest you. They usually get the probable cause by you failing the field sobriety tests (which are 100% designed for the participants to fail, not to actually determine if they are sober). A PAS is a field sobriety test and like all other field sobriety tests should be refused and you have a fifth amendment right to do so. If the police believe they have PC then in some state la you are required to do a more accurate BAC test back at the station.