A safe restricted zone system of a bicycle which can be connected with the bicycle includes one or more projector-sensor devices and a processing unit. Each projector-sensor device can detect vehiclesnear the bicycle, and at least one part of visual security area can be projected on the ground around the bicycle. The processing unit is communicated with one or more projector-sensor devices. Whenone of the projector-sensor devices detects the vehicles near the bicycle, the processing unit generates an alarm which can be aware of by a user of the bicycle, and the one or more projector-sensor devices change(s) the visual appearance of the visual security area. In some embodiments, change in the visual appearance of the safe restricted area includes color change.