I've often noticed that really busy airports (eg T5 LHR) pass me through when later, carrying exactly the same clobber a smaller airport ( eg ABZ) will give an alarm - conclusion - the smaller places change the settings to keep busy..........
Got stopped at Humberside flying back to ABZ with a Stanley knife blade in my briefcase (not I hasten to add knowingly). Had managed to get through ABZ that morning with no problem. A "small" airport may be a relative term.