Back in 1999 the Camry I had had a valet button on the lower left corner of the dash. There was a way to turn the key on, push the button in and then disable the alarm system for the valet. This also worked if the battery went south during the day. What actually happened to me once was that the fob itself had died and I was not using the alarm at all. I parked the car in a hospital garage for a few hours and when I returned, the alarm was set!! Someone else nearby apparently had the same frequency set and had set the alarm. I had to sit there and call the dealer to figure out how to get the car started so I could go home.
I probably just need to play with this new one next Saturday and see if I can figure out the trick if there is one. The battery should last for a couple of years, but Murphy's law being what it is, we ALL need to know how to handle the situation!