Hi, welcome to Just answer! My name is Ross and i will help with your question
There are two sensors at the front either side behind the bumper and one in each door for the side curtain air bags, there is also a seat pressure sensor in the passenger seat so in total there are 6 impact sensors and 1 pressure sensor.
A rear end shunt can set off all or some air bags, it depends very much on how hard the car was hit, the air bag control unit also has a "fail safe" sensor, this needs to be triggered as well as a position sensor, so if the fail safe sensor and for example one of the rear door sensors detected the shunt it would certainly trigger all of the air bags.
I hope I’ve provided the information you were seeking. If you are happy with my service, please provide a rating. If not, please let me know so l can continue to help you. Thank you, Ross.