Patent ID: 7541914

Claim:
A warning system for a motorized road vehicle, the system comprising (1) a mobile telephone which (i) when it is in a standby mode within the vehicle, generates RF signals of a first, transient, type, and (ii) when it is being used by a motorist within the vehicle in a communication mode, generates RF signals of a second, longer term, type, and (iii) does not generate any special RF signal for the purpose of activating the warning system; (2) an activity detector which (i) automatically detects the RF signals of the first and second types, (ii) discriminates between the RF signals of the first type and the RF signals of the second type, and (iii) has a sensitivity such that it does not detect RF signals from mobile telephones outside the vehicle or RF signals from transmitting stations transmitting to mobile telephones outside the vehicle; and (3) a display device which (i) is switched on by the activity detector while the activity detector is detecting RF signals of the second type, and is not switched on while the activity detector is detecting only RF signals of the first type, and (ii) when it is switched on, displays a visible warning signal on the rear of the vehicle.