You been done.
Report them.
Easy solution, disconnect the mains supply to it, you should have a fuse or switch box to turn it off, IT will continue to sound until batteries runs down. After that silent
Then get some one decent, a pir is about £20.
If you lived near Scarborough, I would of done it for £100 Not registered though. BUT £380 they are laughing.
SD
March 2012