A coach firm in Bournemouth has fitted alcometer breathalysers to its fleet.
Drivers at Excelsior coaches must blow into the device when they start a shift and if it detects any alcohol on their breath, the engine will not start.
The "alcolock" device then automatically sends an alert of a failed test to the company via text message and the driver is replaced.
Between 30 and 50 individual breathalyser tests are made at the company each day.
Kathy Tilbury, Excelsior coaches said: "We believe it's a protection method, for our passengers and our drivers.
"The driver blows a breath sample in front of the passengers so they can see, we've had nothing but positive feedback."
Invented in Sweden, the alcolock system is a breathalyser unit, similar to those the police use on roadside checks and is connected to the vehicle's immobiliser.
The system was introduced on all National Express coaches last year.