Purely on the safety side, rather than security. I'm frequently in the position where I become a lone worker. Status wise, I'm considered to be a contractor, carrying out work usually on my own, but in a building with hourly paid and salaried staff and members of the public. However on numerous occasions, the most recent last week, I've found myself locked in, with everyone having gone. I'm talking about theatres in the main, or performance spaces that are large and have many exit routes for everyone. What seems to happen is that the people who knew I was there go home, new staff come on and they forget my presence. A couple of hours later, I pack up to discover the alarm set and the door locked. In this venue, I suspect I'm probably the oldest person, and the one who has been in the place frequently since 84! As such, I know at least 8 ways out of the building that won't trip the alarm, and will auto lock after I have gone out. Sometimes my complete exit involves hopping over a fence because the security grill will have been locked down.
For my own safety, I always have a phone or radio with me so assuming I was conscious I could summon help. If I was unconscious, then it's a different storey.
The idea of having two key holders who must be called out is a new one to me. Is this now a standard? Certainly calling key holders would bring just a single person. It's also common for the cleaners to unlock individually - I'm wondering if this is no longer acceptable.