How should a security company measure KPI?

The product that I want to make and sell is a network security device. I am finding it hard to determine how much value it provides to my potential users. It could easily save them from having their identity stolen which would in theory save them a lot of money. But I don't know how to translate that into a KPI.

So I'm trying to look at this from other angles. How do related businesses measure KPI.

For example, what about companies that manufacture locks. What about companies that manufacture safes. What about back when companies used to sell antivirus software. How would a company like that measure KPI?