Can any of the more experienced guys/gals help me out with this one please. I updated an alarm system over a month ago which consisted of new control panel, remote keypads and bell box. Customer wanted to keep her existing PIR's to keep the cost down. I installed the system and did the usual commisioning inc walk test etc. and everything was fine. Customer called this weekend and said her alarm had started going off for no apparent reason. When I went to have a look the internal PIR fuse has blown. The fuse was the correct rating for the board. Has anybody else come across this before or is it nothing to worry about? Any advice would be much appreciated.