You can do a Wi-Fi sniffer with an ESP8266 and you will be able to know how many smartphones are in the vicinity, in this way you will be able to know in a very approximate way the number of people in the office.

You can see it as an alternative to the deployment of a sensor (whatever the type of sensor chosen) by desktop.

GitHub Porject - ESP8266 WifiSniffer

Best regards.

You can do a Wi-Fi sniffer with an ESP8266 and you will be able to know how many smartphones are in the vicinity, in this way you will be able to know in a very approximate way the number of people in the office.

You can see it as an alternative to the deployment of a sensor (whatever the type of sensor chosen) by desktop.

GitHub Project - ESP8266 WifiSniffer