3451 Car Buzzer Parking Reverse Radar Backup 4 Sensor System Brand new & high quality Easy to install Anti-freeze and rain proof design Helps to prevent dangerous and costly collisions Helps to provide increased safety for passengers， pedestrians， and family members who happen to be around the moving vehicle Featured functions: Measuring the distance by radar Alarm by three step Bi-Bi sound 4 sensors Parameters: Rated voltage: DC12V Operating range: DC9V - 18V Rated current: 20mA - 200mA Detecting distance: 0.3 - 1.8m Ultrasonic frequency: 40KHz Working temperature: -30 to +80 deg. C Sensor color: silver The buzzer sounds in different frequency according to different distances. Details shown in the following: 1 >180cm Safe Mode No sound 2 130-180cm Safe Mode Bi------Bi--------Bi 3 60-130cm Alarm mode Bi---Bi---Bi--- 4 0-60cm Danger Mode Bi-Bi-Bi- Package contents: 1 x Main box 4 x sensors 1 x Buzzer 1 x Power cable 1 x Hole saw 1 x Double side sticker 1 x User's manual