another reason for false car alarms

[dipstick]

I had parked my 2003 X5 at my friend's home in dense city. I was sleeping in the guest room and the familiar alarm went off. I could use the key to reset the car and this happened twice before I just unlocked the car (I could do this from the bedroom) the next day a spider desended from the visor, right by the motion sensor. I grabbed him and threw him out. Problem solved. No alarm the next night. The alarm had gone off unpredictably over the past few weeks and it is now silent.