How far back does swab test detect alcohol?
Swab tests are not used for alcohol detection. Alcohol is measurable via breath, urine, or blood samples. Swab tests are used, among other things, to collect DNA samples.
A swab test can detect most drugs, time periods can range from 2hrs to four day's max. If you have used prior to this period, your mouth swab test will not recognise the presense of any metabolites. Most work places choose to do a random drug test, so changing the results of a swab test would be very difficult.