<ul><li>The package includes the following items:</li><li>60 black sensors and rings; 20 white sensors and rings; 2 drill bits</li><li>20 control centers</li><li>20 power wires and quick conectors</li><li>20 sound beepers</li></ul><br><br>Four ultrasonic sensors mount on the rear bumper, and they are activated when a driver puts their vehicle into reverse. A drill bit for the size of the sensor is included. The beeper sounds when the sensors detect an object. The sound frequency changes base on the detect distance changing. It is very easy to install. No need to layout the wire from the control center (in the trunk) to the front cab.

Sound Only, 4 Rear Drill-in (25 Black) Sensors Car Backup System (SS4)