The backup beeping is arguably the most common complaint Prius owners have. I hate it. It can be changed to a single beep using Techstream or other methods of accessing the car's computer via the OBDII port. Or a dealer can do it, but I hear many of them charge for it even though it only takes a few seconds once they connect their computer. You'd think they'd do it for free to entice you as a customer. But then, when you replace the 12V battery, it will forget and revert to the continuous beeping.
No volume control. I turned it off in my 2010 via the OBDII port using a third party tool (ScanGauge, but there are many others). For my 2012, I just checked off a box on the dealer's list of available customizations, and by magic, it happened. Look up Customizable Features in your owner's manual. It is on page 596 of my 2012 manual, surely your later vintage has seen that book grow additional pages. Unfortunately, my year shows it as being changeable only by the dealer, not the owner. In which case, you will need to employ an OBDII tool, such as ScanGauge (required code available on another thread), or Techstream, etc.
Some history. Toyota ran into trouble with US regulators because the shift lever does not stay in R. The bureaucrats wanted the transmission to clunk, like normal automatics do, so owners would know it was in R. Since nothing shifts when you use R, (Motor/Generator 2 just spins the other way) Toyota would have to build a device to make a clunk for no reason. They countered with a Beep, which would be cheaper. The best time to set the beep to one beep instead of continuous beeping, is before you buy. The salesman will agree to anything to get the sale. I set mine with a Scangauge, I have set several others, it just takes a minute. If you can stand it until the next service, ask for it then.
I used Carista and a cheap bluetooth OBDII scanner to change my settings. You get to change quite a few other settings with Carista as well. Carista – OBD2 vehicle diagnostics, customizations, coding & tools The bluetooth OBDII scanner I bought from e-bay for like $5.
Is Carista worth it? Anywhere I can see a list of options that I will get with a 2015 prius? Don't want to pay $39 to turn off the beeping alone, but if I can access a bunch of other useful stuff it would be well worth it
EDIT: found more info on their website. I would like to change the behavior of the Auto climate control, like change it to always be on the mixed (floor and dash) setting. Looks like it's not that in depth but there are a lot of settings to play around with
