i have done this in the past, first thing to do is to get HR to write a policy and then get the Union/workers reps to agree to it. we used the breathalysers that the police use and whn calibrated they are very accurate. we were trained by the supplier of the equipment and testing was only done internally by managers. the machines print out a result on paper there is a computer programme that you can use to generate random numbers which is what we used and then matched against the staff name. we then tested within the month, if there was a fail then we retested 20 mins later, second fail they were suspended and disciplined any questions PM me