What is this?

[aislinn]

This is on our original kitchen door frame leading to the back porch. Maybe a button to let someone know when the door was open?

[Gothichome]

I have no idea, is it spring loaded? If so, my only thoughts it’s a fancy automatic boor opener. Once unlatched the spring pushes the door open. Just a wild guess.

[Lily left the valley]

I'm having a hard time seeing the hardware because of the soft focus.

Although the door hinges are on that side of the door now, they might not have always been. There may have also been a screen door there at some point, even if only seasonally.

If the center half round portion depresses when you put your thumb on it, it may be an early form of a ball catch. Is there a matching depression of any kind in the edge of the door itself on the hinge side?

If the center portion of that hardware is raised but nothing behind it, it could be a soft catch/spring catch/snap catch for a (possibly screen) door. So instead of having a hook and eye, it would keep the door closed by there being another piece that latches around that raised piece. This latter possible is more likely if the door swung open opposite from how it does now, given the hinge in the image.

[aislinn]

It does depress, but nothing matches on the door. I took a video but I guess videos aren’t allowed on this platform! So when the door closes its flush with the frame, but when it’s open the rounded part pops out. Such a mystery!

[Manalto]

Is the image supposed to be vertical? On my monitor it's out of focus. I have no point of reference; it looks like I may be seeing half a hinge, but there's no way of telling where on the door or doorframe it is.

[aislinn]

Sorry! Im not sure why my photos are being flipped when I post them, but yes it should be vertical. Here’s another photo. It’s at the bottom, below the lowest door hinge.

[mjt]

is it connected to anything (i.e., are there wires on the back side)? Could be a light switch; light is off when door is closed and on when door is open...

[Manalto]

Ah, much better. (but I still don't know what it is) I tend to agree with mjt that it's some kind of switch, but I'm as baffled as you are.

I found this:

https://www.youtube.com/watch?v=PPbAW3KFPfY

[aislinn]

So I’m wondering if maybe it was part of an alarm system. Our house used to have one (there’s a box in our utility closet with the name of the security company). Maybe when the door was opened when the alarm was set this would trigger it to go off?

[Manalto]

I wondered that myself but was reluctant to mention it because I don't know how far back home security systems go. Does the box look like it's about the same vintage as the button in the door jamb?

My security company told me that criminals may not come in through the door but they always leave that way, so it's a good place for a sensor.