system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How does Google determine how busy a business is in real time?

If you've ever Googled a local business, you have probably seen a graph, indicating the average traffic (Popular Times) at a specific hour, during their normal business hours.

There is also a "Live" function, that shows how busy they are at that exact moment. How is that information updated in Google in real time? Does someone actually manually update this information regularly or is there some sort of algorithm that makes this determination?
gpt
People with phones using Google Maps location services.

When you've got a smartphone with Google Maps on it Google can periodically check in on the location of the phone if more people happen to be at a certain location within a given time window Google can assume a location is busier. It's also how the live function of it works. This is also partially how Google Maps can get some data on general traffic conditions.