Pocket Radar products are Doppler speed radar systems.They work as a speed detector by emitting a small pulse of radio waves in an invisible focused beam, similar in shape to a flashlight beam.When the radio wave hits an object that is moving towards or away from any of the Pocket Radar’s, a small amount of the wave reflects back.The moving object modifies the reflected radio wave based upon how fast it is moving directly towards or away from the Pocket Radar unit.The unit then receives the reflected radio wave and compares it to the original transmitted radio wave. It then calculates the speed of the moving object based upon the difference between the two radio waves.Note that each Pocket Radar model, like all Doppler speed radars, can only measure the speed of a moving object that is reasonably close to in-line with the direction of the radio wave beam. They cannot measure any motion side to side, across the radio wave beam. (NOTE: Never put yourself or others in a position where anyone could be hit by the moving object!)The focused beam comes from the radar lens on the back of the unit directly behind the display.Hold the unit up vertically like a camera phone with the beam from the radar lens directly in line with the moving object you want to measure. Then “Tap” or “Hold” the larger button, like you are taking a picture, while the target object is in motion. The speed(s) will appear on the display.If the unit’s display is turned off and you missed the last speed reading, just press the small black button and it will re-appear. Continued tapping of the small black button will recall previous speed readings.