total newbie- How to tell if my 09 Prius has an alarm?

Best way to approach this is do a search like the screenshot below, then read up on all the discussions over the years about tilt sensors and that will answer all your questions, as well as help you realize how unhelpful or wonky some of the Prius Chat commenters can be at times:

 

Get a cat shield. To test it out if you have a (functional) alarm, you may or may not have an aftermarket one, lock the car and give it a nice push a couple of times to see if that triggers it. Since most cats can be taken out in seconds, and basically all they need is a Jack and a sawzall, it wont be enough to trigger an alarm.