Alarming when starting

I have a 2012 Prius, with key fobs and push button start. Recently my horn has been sounding 3 time every time I start it. It starts immediately and the moment I press the start button, it there are three rapid beeps. This behavior is the same if I have the fob actually touching the button also. I can use either fob and the results are the same. I have changed my fob batteries twice, with different brands of batteries, and still no change. I'm up for any suggestions you might have.