An alcolock has proved to be effective: it leads to less recidivism than suspension or revocation of the driving licence. This effect is often only observed during the period in which the alcolock is present. However, if the causes of alcohol abuse are also tackled, for example by wider deployment of an integrated alcolock programme, the measure may also have more lasting effects. An alcolock is an alcohol tester that is connected to the starting mechanism of the car. The tester works as an immobilizer. It is only possible to start the car after passing an alcohol test. An alcolock is usually part of an alcolock programme that does not only include installing an alcolock in the car, but also involves an accompanying educational or medical programme. Since 2015, CBR has no longer been allowed to impose the alcolock programme on alcohol offenders in the Netherlands.
A study by WODC Research and Documentation Centre shows that the recidivism rate in the Netherlands is lower than for other measures, even after removal of the alcolock  . Participation in an alcolock programme, reduces the recidivism rate of drink driving by 50% in the two years after termination of the alcolock measure.
Various international studies in the period 1990-2020 also show that the recidivism rate of users of an alcolock is 65-90% lower than that of drivers whose licences were suspended or revoked   . In the studies, no evidence was found for an effect of the alcolock after it had been removed from the vehicle    . The alcolock programmes in Sweden   and the US  showed that the programme did result in lasting changes, both in alcohol consumption and drink driving. According to the Swedish researchers, these lasting changes are the result of the integral character of the programme: it addresses the cause of the alcohol problem, and not just the symptoms. This outcome corresponds to the US findings: if an alcolock programme is coupled with psychological counselling to deal with an alcohol problem, reduced recidivism lasts from one to four years after removal of the alcolock .
In addition to a measurable effect of reduced recidivism, US studies also found proof of a direct road safety effect: in states with an alcolock measure the number of alcohol-related road deaths is significantly lower than in states without such a measure    . In Ireland, the cost benefit ratio of introducing an alcolock programme for repeat drink-driving offenders was estimated to be one to six .
Ban on alcolock
In March 2015, the Dutch Council of State determined that CBR could no longer impose the alcolock programme. The main argument was that imposing the programme under administrative law, without the intervention of a judge, could have disproportionate effects in a substantial number of cases. In 2018, after consultation of several experts, the Minister of Justice and the Minister of Infrastructure and Water Management concluded that other measures were preferable to reintroduction of the alcolock programme (under criminal law) . The ministerial arguments against reintroduction of the alcolock programme were that the target group eligible for the imposition of an alcolock would be small (30 – 2270 persons in the scenarios that were examined), that the costs of an alcolock are high and that the alcolock is susceptible to fraud. The ministers put forward the option to increase the penalty for drink driving and lowering the BAC for the examination of fitness to drive as alternative measures for the alcolock. See the question How effective are heavier penalties?.