I think the way the article worded it is confusing. Every staff member wears a photo ID badge, which is pretty common at most schools. At this school, their photo ID badges have a little button on the back. When that button is pressed, it activates the system.
I’m sure the buttons have little batteries inside them, probably similar to the type of battery in a smoke alarm. These types of batteries can last for years. However, many school districts issue new photo ID badges to staff each school year, so perhaps batteries are being replaced at that time if needed.