Alarm/door sensor problems

[andynx.19]

hello
i have a 56 plate passat and have problems with the alarm going off for no reason. On the dash it shows the front passenger door open when the door is closed and some times strobes, me and my mate changed the door lock module thinking this would cure the problem. But the problem still exsits. my mate has his own car diagnostics and the oly fault code it shows is the rear left passenger door lock module, but ive not seen the door open on the dash like the front passenger door. could any body shed any light on this

thanks