They just 'beep'. They are not tied into the nav screen. Here's an excerpt from the manufacturer's web site.

"THE SYSTEM IS ONLY OPERATIONAL WHEN THE VEHICLE IS IN REVERSE. WHEN A TARGET, SUCH AS PARKED CARS, TREES, AND GARAGE DOORS ARE DETECTED IN THE COVERAGE AREA OF THE FOUR SENSORS, THE SYSTEM WILL GIVE AN AUDIBLE ALERT TO THE DRIVER VIA THE ALARM UNIT MOUNTED IN THE INTERIOR OF THE VEHICLE.
WHEN THE VEHICLE IS PUT INTO REVERSE, THE SYSTEM WILL SOUND TWO QUICK "BEEPS" TO ALERT THE DRIVER THAT THE SYSTEM HAS BEEN ACTIVATED. THE SYSTEM WILL ALERT THE DRIVER TO THE PRESENCE OF A TARGET WHEN IT IS WITHIN ONE OF THE THREE DETECTION ZONES. ZONE 1 IS THE
FIRST DETECTION ZONE AND COVERS THE DISTANCE FROM APPROXIMATELY 3 FEET TO 5 FEET AWAY FROM THE REAR BUMPER. THE ALARM UNIT WILL GIVE A SLOW BEEPING SOUND IF A TARGET ENTERS INTO THIS ZONE. ZONE 2 COVERS THE DISTANCE FROM APPROXIMATELY 1.5 FEET TO 3 FEET, AND THE ALARM UNIT WILL GIVE A FASTER BEEPING SOUND WHEN THE PASSES INTO THIS ZONE. ZONE 3 IS THE FINAL ZONE AND COVERS THE AREA FROM 0 TO 1.5 FEET AWAY FROM THE BUMPER. THE ALARM IS A CONTINUOUS TONE WHEN THE TARGET IS DETECTED IN THIS ZONE. WHEN THE TARGET MOVES OUT OF THE DETECTION AREA, THE SYSTEM WILL STOP ALARMING. THE PARKPILOT ALERTS THE DRIVER TO MOVING AND STATIONARY TARGETS. THE SYSTEM IS DEACTIVATED WHEN THE VEHICLE IS TAKEN OUT OF REVERSE GEAR."

See the following link for more information.
http://www.rostra.com/ParkPilotParkingAide.htm