A guy I made a website for a looong time ago sold systems like that. The system he sold had some really neat tricks to avoid needing to be connected to a networ

A guy I made a website for a looong time ago sold systems like that. The system he sold had some really neat tricks to avoid needing to be connected to a network and the like. The main entrance had the only networked badge system. What it'd do is when you entered the building it'd write an update list to your fob. When you then open any of the non-networked locks they'd grab the update list from your fob. This way things like revoking access to fobs or adding new fobs to the system would get to all the doors pretty quickly without them needing to be connected to wifi or whatnot. Of course this also makes it feasible for the locks to run on batteries for a long time. The next trick the locks did was when you unlock a non-networked door it'd write its battery state to your fob. When next operating a networked lock it'd pass the battery state along to the main database. Hey presto you're getting low battery alerts, and there's still no always-on network slurping battery life. In case of a power outage the reception people could let people in the main door, and all the other locks in the building would keep working as they always have.