The other addition to Reminders in iOS 9 is the ability to create reminders for when you’re getting in or out of your car. These reminders use a Bluetooth connection in your car to determine when your device has entered or left the vehicle, which can be useful to remember to do something before driving or immediately after stopping.
I use reminders often to remind me to do things when I get home, or when I get to work. Now I can use reminders when I get in or get out of my car. You can set these reminders using Siri, or by specifying your car as a location:
I tried this with my 2011 BMW, which has no aftermarket modifications to the stereo, and it worked no problem. Very cool.
In combination, my experience and the image above seem to answer Federico’s follow-on question:
To this day, Apple hasn’t clarified whether car reminders in iOS 9 require CarPlay or can work with generic car Bluetooth and third-party accessories.
Sure does work with non-CarPlay cars. Moreover, if you happen to have your phone paired to more than one car, the verbiage on the image above seems to indicate that these reminders will fire when getting into or out of any car your phone knows about.