Abstract: A proximity sensor may be used as part of a vehicle blind spot detection system. The sensor is configured to transmit multiple radio frequency (RF) signals of different frequencies, receive reflected RF signals, and supply intermediate frequency (IF) signals. Each IF signal is representative of one of the reflected RF signals, and each reflected RF signal corresponds to a transmitted RF signal that was reflected by an object within the sensor detection region. The sensor uses the IF signals to determine whether an object is within its detection region and its movement direction.