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OK, this is getting interesting. I've done some tests.

First, some pictures [1].

The first picture is the front of the TV remote and what I presume is the window in front of the IR diode.

The second picture is what is supposedly the location of the IR sensor on the monitor.

The third picture is my hand attempting to block the IR emitter on the remote.

Here is what I've found.

1. If I block the emitter with my hand the remote has no trouble turning the TV on and off. Even if I've blocked it with my hand and am holding the remote behind the couch so there is no line of sight to the TV it still works.

2. It also still turns the monitor on and off, but the range is greatly reduced. I have to be within a meter of the monitor.

3. Blocking the receiver with a finger is similar, but the range reduction is more. I have to have the remote within maybe half a meter.

4. Blocking the remote with electrical tape has no effect on its effectiveness with the TV.

5. Blocking the remote with electrical tape almost completely prevents it from affecting the monitor. Maybe 1 in 20 times it will still turn the monitor on/off if near the monitor.

6. Blocking the receiver with electrical tape is similar.

7. Blocking the receiver by hand or electrical tape has no affect on the monitor's remote controlling the monitor.

8. The TV remote can turn the TV on and off and the monitor remote can turn the monitor on and off even if I go down the hall an into the bathroom and close the bathroom door so there is no chance that any IR signal is making it to the device.

9. The monitor remote does not turn the TV on/off even if held near the TV.

10. I also have an Amazon Fire Stick and its remote can turn the TV and monitor on and off. It uses IR for TV control functions (and RF for Fire Stick control).

11. As with the TV remote my hand fails to block the Fire Stick remote.

From this I think we can draw some conclusions but also some questions are raised.

• The TV remote can fully operate the TV using RF. The TV also responds to IR.

• The monitor remote can fully operate the monitor using RF. The monitor also responds to IR.

• The RF for each remote includes specific enough device identification that they do not operate the wrong device. The IR does not.

• IR is hard to block. Why doesn't my hand stop it? With the TV remote the window is big and curved so I could see some of it not being quite covered, but the Fire Stick remote has a smaller window that is much flatter. When pressed tightly into my palm it should be completely covered.

• Electrical tape almost seems to completely stop it, but I did still have an occasional signal get through.

• When turning the TV off from the couch I should be able to stop it from affecting the monitor by simply covering the window with my palm. Even though that apparently still leaks enough IR signal it reduces the effective range, which should be enough to stop it from affecting the monitor. It will still work with the TV via the RF signal.

[1] https://imgur.com/a/LcsqK4j