While this all seems to be voluntary in your case, your method leaves open the option of you fooling them, by leaving your cell phone in your desk drawer. They already are talking about sub-cutaneous implants for everyone. Right now, it's aimed at school children( and pets), but you can bet that they will push it for all employees, ostensibly for insurance and safety purposes.
in reply to Bluetooth people presence detector :)
Then there are the secret RFID devices they are coming up with, like on badges, sewn into clothes, etc.