July 21, 201114 yr What is that button on the upper-left part for? Not where it says HRN(Horn) but where it says SRN? Never saw that... Or the sound it makes Ooo! That's for the manual, he does it at 00:34. Or if the SWP is toggled the SRN button starts the SWP pattern. Sorry for being all excited, but I have a thing for lights and sirens ha ha.