occupancy system

I am currently working on an occupancy system where i am trying to implement motion detection using pir and parallax ultrasonic sensor to show occupancy in a room,is it a good idea?

afterwards i would like to send those data into a device called a jace 8000 which talks modbus tcp/ip which is layer 7 protocol, i have the stack(modbus tcp/ip stack or library) and struggling to link it can anyone help?

is it a good idea?

It will certainly be a good learning experience.

Solve that problem before you worry about sending the data somewhere else.

A PIR is a MOTION sensor.
No motion, no sensing.

An ultrasonic sensor is a distance sensor.
It might be able to see if someting is there that wasn't there before.

Try a Grid-eye (Google it).