Does it control anything that you need? If not, you might as well just disconnect the red and blue wires from the transformer secondary and forget about it.

BTW, I see some code violations in that wiring in the first photo - cables not secured within 12" of box and probably also not supported properly, and transformer primary wires improperly run unprotected though an NM connector. It's a generally sloppy, unworkmanlike installation. I hate to think what might be inside that box. At least this part of your house appears to have been wired by a low-clue DIY.

I’m not understanding if the light/lock are close to the the mess of wiring by outside do you mean outside the basement or outdoors? What’s the layout?

The light/lock are connected to the mess of wires, i.e. the mess of wires are connected to the back side of the plate. On the front side of that plate are the light and the lock. The light and lock are outdoors on the porch side. The transformer is in the basement, with wire path (not shown) going through the floors and up towards the porch.

DavidR, cables not secured within 12" of the box? how do you mean? The wires are within 12" of the box. Do you mean they are not secured to or within some other box?

Gosh, I hope it's not security. It's a rather crap lock which really doesn't matter since all you need is a screwdriver to open it up and defeat it,

Cables (with small exception) must be supported in place within a foot of the box that they are terminated in an every 4.5 feet thereafter. The box itself doesn't count as support. While lying on the ceiling joists counts these don't look like they are. They also should follow some building surface rather than taking off through midair like that.

"cables not secured within 12" of the box? how do you mean?"

In exposed work like that, and in concealed work where the cable wasn't fished, cables are supposed to be fastened (usually with staples) to the building framing within 12" of the box. Yours aren't.

I'm also not too impressed with the way that box is mounted, or with the cable that loops under the joist.

It's all hack work, and it suggests that other code violations may be present.

As for your keyswitch and pilot light, it could have been controlling anything. Your guess of a security system is as good as any.

If it has no purpose now, and all the wiring is low voltage, you may as well disconnect it at the transformer, cut the wires short at the outdoor point, and abandon the wiring in place. You can replace the outdoor plate with a plain one, or close up the siding hole in whatever way works.

Or repurpose it as a doorbell, if you need or want one. :)