after market alarms DO NOT work well with BMW circuitry. If u search the forum, there are lots of owners who complain about this and wonder why...
if u absolutely need to have the sensitivity alarm, I suggest you connect only that part of the alarm system that sounds off when ur car is touched... DO NOT for any reason have the ignition disable & door lock function- you will be in trouble if u do.
** the alarm installers will scratch their heads on this one... but if they know their circuitry basics, they will understand. If not, u hvnt found the right alarm people