Not sure where you're based, but for UK cars, standard equipment on all A5/S5 models is listed in the brochure as:
"Anti-theft device - Thatcham Category 1 approved". which has to include both an alarm and an immobiliser.
Not sure if the A5/S5 has the inclination sensor (which is only required for motorbikes) however my old S4 had this, so would think that all Audis have it. There were 2 switches in the driver's door to turn off either the interior motion sensor (should you want to leave an animal or child in the car but still lock it) and the inclination sensor, for loading the car on a tow-truck, so the alarm doesn't go off.
Maybe someone with a current car will know if these features are still included, but I can't see why Audi would delete them. Generally Audi are considered to have one of the best factory-fit alarm systems on the market, and when What Car tested new cars in the UK a little while back, the Audi A4 was the only car of the group tested that their 'tame car thief' couldn't start and drive away.
Mine has no alarm on it, it is an option, however it has a satellite tracking and immobilization system as standard. You can call the service and they stop the car, and if it has been stolen, it flashes the warning sugnals, honks the horn if the car is running, and immobilizes it if the engine is switched off. Also includes GPS localization. This is standard for France, the service is free for the first two years ( lots of arjacking on any audi that has an S or RS badge).
It also has a standard anti theft immobilization system that keeps the car from being hotwired by coding the system through the key ( standard on lots of cars)....