Abstract: The electric power consumption of a vehicle having its own power source and travelling on an unbounded path is monitored; and, when this power consumption remains substantially constant for more than a predetermined period of time, the invention sends a signal to the driver, to which he must respond with predetermined accuracy and in a predetermined period of time. Failing this, the invention gives the operator a warning display and repeats the test which, if failed repeatedly, results in the equipment giving an alarm perceptible to those outside the vehicle, by the horn and/or flashing lights. In addition, the invention can preserve a record of the driving conditions and test results and can provide coded access to operation of the vehicle to prevent unauthorized entry. The invention can also provide a test of alertness which the driver must pass before actuation of the vehicle can be initiated.