An object detection system comprising: - at least one first transmitting unit to be located near the object, the first transmitting unit having an identity and being provided with a transmitter for transmitting a first signal with a communication protocol and representing the identity of the first transmitting unit, and - a receiving unit (11, 18) provided with a receiver for receiving the first signal, the receiving unit being adapted to generate a second signal in case the first signal represents the identity of one of said at least one first transmitting unit, wherein the first transmitting unit comprises an active transmitting unit, provided with power driven means for transmitting the first signal in the form of a radio signal and wherein the first transmitting unit comprises a power source, wherein the first transmitting unit comprises an electronic data processing unit, and wherein the first transmitting unit is adapted to receive an activation signal, the electronic data processing unit being adapted to activate transmission of said first signal in response to a recognition of the activation signal, wherein the first transmitting unit is adapted to operate in a first mode and a second mode, the power consumption of the first transmitting unit when operating in the first mode being lower than the power consumption of the first transmitting unit when operating in the second mode, characterized in that the first mode is a listening mode, wherein the first transmitting unit is listening for any communication following the same communication protocol as the first signal, and the second mode is a data processing and transmission mode, and the receiving unit being adapted to receive the first signal when the distance between the first transmitting unit and the receiving unit is within a predetermined interval. - at least one first transmitting unit to be located near the object, the first transmitting unit having an identity and being provided with a transmitter for transmitting a first signal with a communication protocol and representing the identity of the first transmitting unit, and - a receiving unit (11, 18) provided with a receiver for receiving the first signal, the receiving unit being adapted to generate a second signal in case the first signal represents the identity of one of said at least one first transmitting unit, wherein the first transmitting unit comprises an active transmitting unit, provided with power driven means for transmitting the first signal in the form of a radio signal and wherein the first transmitting unit comprises a power source, wherein the first transmitting unit comprises an electronic data processing unit, and wherein the first transmitting unit is adapted to receive an activation signal, the electronic data processing unit being adapted to activate transmission of said first signal in response to a recognition of the activation signal, wherein the first transmitting unit is adapted to operate in a first mode and a second mode, the power consumption of the first transmitting unit when operating in the first mode being lower than the power consumption of the first transmitting unit when operating in the second mode,