grouch

The wife and I were shopping and I loaded an oversize purchase in the back with the seats folded down. When I started the car, an alarm sounded.
We thought it was a cell phone, but it was the car. No dash indication of any kind. After several failed attempts to stop it, my wife unbuckeled her seat belt and it stopped for about 10 sec. then started up again. I turned everything off, got out and open/closed every door. When I started it again, no alarm.!!! My wife said it was mad because we put a new toilet in the back and the Lexus felt threatened.
I've heard alarms before but never one that sounded like a cell phone. Any ideas? 04' RX330