I think it depends on the units. Does this mean a blood alcohol content of 0.1% (ie 0.1g per 100ml)? From a quick google search that would be enough to make someone slur their speech and appear drunk so I’d imagine an “effectively zero” limit is far below this. You’d need to compare the UK mg/ml limits across blood, alcohol and urine with the Swiss equivalents to be sure. I’ve not heard of anyone failing a med screen for alcohol. What has caught a few people out is the presence of “illicit” substances which can linger in the blood stream for weeks.