Just knock

In my office, I sit with my back to the door. I don't like doing that, but it's the only way I can sit. My chair back is high and obstructs the view of my phone, meaning that people can't tell when I am talking on the phone. This would not be a problem if people walked up to my door, knocked, waited for me to say "hello" or some kind of response, and then proceeded into my office.

Instead, I am constantly bombarded by people walking straight into my office, without knocking, chatting away at me [in some cases very loudly] like I am able to listen. Not only are they disrupting my phone call, but they're also wasting their breath because I am trying to concentrate on whatever problem the person on the phone is having. Other people walk in so quietly, without knocking, that by the time they are standing beside me and begin to speak, I've jumped 10 feet in the air because they scared me. I am often absorbed in my work and don't hear someone enter. My co-worker has to answer the "Is she on the phone" question multiple times per day. I can only imagine how aggravating that must be after the 10th time in the run of a day.

Knocking and waiting for a response doesn't seem to be in some people's realm of capability. How about this? Walk up to my door, come in, and step two steps to the right, then they would be able to easily see if either my in-use light was lit, or they'd be able to see the receiver's cord stretched out, indicating that I am holding the receiver to my ear. Simple? You'd think so.

This has been annoying me to the point where I have thought about trying to place a light on the wall above my desk that will indicate when my phone is in use. I've searched around on the internet for such a device, but all I can find are circuit diagrams of how to make one.

I just don't understand what's so hard about knocking before entering.