A sensing and indicating device is mounted at a fixed location and uses transmitted and reflected acoustic or electrical energy to determine the distance between the sensor and an approaching vehicle. The sensor provides visual and/or audible indication of the distance between the vehicle and the sensor. The driver of the vehicle uses that displayed or audible information to locate the vehicle within a defined space or envelope, e.g., within a garage. The sensor and indicator may also be located laterally with respect to the vehicle so that the distance between the vehicle side and the sensor can be determined whereby the vehicle can be located laterally within the defined space or envelope. The device remains active at all times, precluding any need for manual intervention to activate it, without compromising power consumption. A distance dependent means for dynamic desensitization of the receiver subsystem is provided so as to ignore reflection artifacts from irrelevant off-axis objects close to the sensor and to avoid false triggering due to ringing within the sensor. The distance dependence of the desensitization is implemented by using an exponentially decaying reference signal as a dynamic detection amplitude threshold for comparison against the amplitude of received echo signals for a predetermined period of time after exciting the sensor with a transmit pulse. Shortened transmit excitation burst times are also used when measuring at close ranges to reduce sensor ring time.