im not 100% but i had a problem like this once i had a standard alarm and fitted an aftermarket alarm too , the problem was that i had to disarm the 1 first and arm the other first or the 1 would affect the other and set it off ,i.m pretty sure that if you are not happy with the standard alarm then a reputable alarm installer could disable the factory one and install another 1 of your choice, then reverse the procedure when you sell the car.