Sounds like he wants SONAR and not an audible alarm for people outside the truck??
Go with the camera.
I like sex, drugs and automatic weapons. That's why i'm a dues paying member of the Libertarian party. Struggling to keep the government away from messing with the above.
My Wife has her own vice.
My bad yeah back up lights derp.
My T.P. wheeling and dealing feedback is here.
Opinions are like assholes, everybody has one, and it stinks more than mine.
Yo Homie, That my chainsaw ?
Pati, improbe et vince
Camera is next, that would be balls. I hate backing up even when I run and look in back, people are morons with or without kids, they let em just walk right in back of the truck. Etc.
Honk horn off and on while backing up.
or
Go to Lighthouse in commerce city, pick up a GOOD backup alarm.
Wire in a backup alarm triggered by your backup lights, like was mentioned earlier, then wire in a weather-proof toggle switch back by your tailgate, inside the bed so you can turn it off when not needed.