RDD immune anti-radars are capable of detecting and responding to the presence of Radar Detector Detector (RDD) devices, which are used by some police forces to detect the use of anti-radar in cars. If an anti-radar is "immune" to an RDD, this means that it is able to either remain undetectable to the RDD or take action ( e.g. automatically shut down) in the event that an RDD is detected.