Is there an audible difference between each sensor or do you have to look at the unit and see the number displayed?
This looks like the one I bought last year.
To answer the one question, you can assign different chimes to the sensors. The only issue I’ve had is that on sunny days, shadows will trigger the sensor, so you might want to put it in shade to begin with.
Or you can hang a tennis ball from some fishing line. 100% reliable and requires no electricity.
This is an alarm for when someone crosses an imaginary line or your driveway to alert you, not a sensor telling you how close you are to a wall or distance