On the '99 Camry you can replace the battery yourself and no reprogramming is necessary. You only need a small philips head screwdriver. My TDS now arms itself sometimes. I was stranded last week and had to get a ride home and then return with the key fob. I’ve decided to carry the fob with me all the time to avoid spending money to get the TDS fixed or disconnected. The battery will cost less than ten dollars. I drive the same car. I was thinking that maybe it happens because my driver door lock usually sticks when you hit the button to lock or unlock it.
My alarm is NOT automatically set upon you locking the door by any method other than the key fob (as it is with my wife’s 2010 Camry). The dealer would love for you to bring the car to them for them to work on, but it is simply not necessary just to change the battery. Since we have a malfunction with the alarm itself we may need dealer intervention or, preferably, a mechanic who knows his/her way around a Camry.