NOVELTY - The device has an electrical capacitive sensor (5) connected to a logic controller (3). A comparison unit (7) receives an output signal (Ct1) of the sensor, detects crossing of a prerecorded limit by the signal and counts number of crossings for a unit of prerecorded time. The comparison unit compares the number of crossings with a prerecorded threshold, and provides a control signal by a windscreen wiper operating unit (20), where the control signal adopts an active state (A) based on the number of crossings exceeding the threshold.    USE - Environmental parameter detecting device for use in a handle of an outer door of a motor vehicle for detecting an environmental parameter i.e. rain state, at an exterior of a cab interior (all claimed) of the vehicle.    ADVANTAGE - The configuration of the comparison unit permits controlling of the windscreen wiper operating unit in response to the approach or presence of material mass such as water drop, at any moment, when the driver is seated inside the stationary vehicle and when the vehicle is moving, thus preventing the dissipation of energy required for maintaining the device in monitoring state. The device does not have additional selective interrupter so as to reduce the complexity of the device. The device can be mounted on the vehicle in an easy manner. The configuration of the device provides better compromise between simple and reliable detection of the environmental parameter and consumption of power necessary for supplying the capacitive sensor when the energy is drawn from a battery of the vehicle.    DESCRIPTION OF DRAWING(S) - The drawing shows a simplified partial schematic view of a detecting device embarked on a motor vehicle for controlling a windscreen wiper operating unit based on a selective detection of an environmental parameter.    Active state (A)    Output signal (Ct1)    Logic controller (3)    Electrical capacitive sensor (5)    Comparison unit (7)    Windscreen wiper operating unit (20)