Car Alarms: Viper Car Alarm (1995), viper dealer, indicator light

Question
Last summer, my father gave me his '95 LeSabre with installed Viper (300?) system (disabled, with indicator light on). Last night my son tried to start the car while he was out shopping but somehow the alarm had become armed.  He did not have the remote with him.  A technician from the nearby Viper dealer turned the ignition key to ON, found the valet switch and re-disabled the alarm.  

QUESTION:  how could the system have become armed all of a sudden?  The tech thought the valet switch might have been jarred accidentally to its armed position, but wouldn't that action have had to be synchronized with turning the ignition key?  

Answer
Yes but also if the car was powered down, (new battery,
or if it was jumped possibly. Low voltage can change the mode.

Other then that, I can not think of anything that would
have changed the mode/status.

You may want to repair/replace the system at this point
to be safe.

Let me know what you find out.

ALARMTEK
www.USCARALARMS.com