How do i stop the car ALARM?

My neighbors car alarm is driving me crazy. it just started to go off and it has the most annoying car alarm sound i ever heard. it's like nails on chalkboard annoying. REALLY PAINFULL. he just got this brand new bmw 7 series and it's driving me INSANE with the car alarm i feel like breaking the car. my neighbor isn't even home so what do i do the alarm DOESN'T STOP. what can i do to stop it?