bmw 530d auto car alarm?

hi
i have trouble with the alarm. yedsterday i locke the door using key in the door- CL worked ok....got my daughter...on way back i tried the remote unlock- didnt seem to work so put key in door....doors opened but car alarm+++ so tired manually lock unlock...tried remote fob...but nothing and larm doesnt stop...even if the beeping not going off eh lights still flashing...had to disconnect from the car battery terminals last night...today reconeectd the batter and same prob
have tried reprogramming the car key...but no difference...at a loss...bmw dealership tells me key fob battery is lifetime but they can replace the whole key at cost of 160...too much for me......any ideas????