Assuming the alarm for a Scenic 1 is the same as on a Meg 1, when you press the button on the ignition key, hazards flash, and the alarm arming is 1-2 beeps. To disarm (when unlocking the car) flash and beep. The door/boot open warning is beep beep beep, if you do nothing the alarm siren kicks in, hazards flash. Also, where there is a CAT1 factory fit, you have 30 secs to start the engine or it will immobilise. To remobilise, you have to (while sat in the car) lock and then unlock the car, then you can start the engine. If you are not getting the arming/disarming beep-beep, or the audible door open warning, then either you have no CAT1 fitted, or it has been disconnected/stopped working.
Karen xx