Help me understand what is happening with rs232

Question

Do it yourself

I'm trying to see what is being transmitted between pieces of security equipment. Logic zero is low, about a volt.
With arduino I boost and invert the logic and feed to the Tx of the rs232 port. Logic zero 0V, unit 5V.
After the equipment starts transmitting a small packet of data, the Serial Port Monitor writes some garbage to the log, even when the wires are physically disconnected from the COM port connector. What is happening and how to fix it?

Answer 1

To begin with:
1. Nothing is sent to Tx, information usually comes out from there.
2. Information is fed to Rx.
3. A physically disconnected Rx has a high impedance and can catch anything. In particular, the weather at the equator.

Answer 2

They described very badly what they inverted, where what levels, etc. ...
Then we will advise.

Answer 3

Security equipment usually drives everything in RS485, not RS232. They are very similar, but incompatible.
485 has a much lower speed, greater range and can work like a tire