The breathalyser was introduced into Ireland in November 1969 along with new drink driving laws.
The device had already been in use in the UK for two years. Gardaí now had the power to make suspected drink drivers breathe into it and, if the crystals turned from yellow to green, bring them to a Garda station where they would be obliged to give a blood or urine sample.
Eddie Barrett reports for RTÉ News on the new legislation on 2 November 1969. Other measures include a blood alcohol limit of 125 mg. Barrett says that state pathologist Dr Maurice Hickey estimates a man weighing 11 stones would reach this limit after drinking at least two and three quarter pints or four small whiskeys, but no one knows for sure.