Apparently you completely failed to understand how the security system works. If it only triggers when someone takes multiple items that weigh the same and scans them as fruit/veggies. Therefor the only way for it to give a false positive is for someone to coincidentally buy more than 2 different fruits/veggies that happen to weigh exactly the same. Seriously, what do you think the odds of that happening are? Pretty much negligible. The system certainly isn't perfect, as it only catches people stealing multiple of one item, but it certainly isn't going to give a lot of false positives. The security guard didn't ignore the alarm because of false positives encouraging lax behaviour, they ignored it because they are an inept buffoon. Even if the system gives out false positives ten times a day, they still should be checking, because that's their fucking job, the whole reason they are getting paid. If they are going to not bother checking because of a false alarm earlier, then they are fucking incompetent and should be looking for a different job.