Does Your Car Need an Interface Module?
The majority of today's vehicles come from the factory with an anti-theft system intended to prevent hot-wiring by thieves. Most of these vehicles look for a special key to be present in order to start the engine. Some newer vehicles even have a push-button start that is aware when the driver’s key is present somewhere in the vehicle. During remote start, obviously there is no key present, so an interface module is necessary, to let the vehicle know it is OK to remote start.
In addition, most newer vehicles control power door locks and anti-theft or security features by sending digital signals over a network called a databus. By interfacing with this databus, your new Viper system can control factory features – right from your Viper remote!
It's easy to find out if your vehicle needs an interface module: simply select your vehicle below.
this is from the viper website, assume others have come up with the same.