By now, it should be fairly apparent that I am not a huge fan of having glass in or around doors. Sure, you are likely to have glass somewhere on your first floor, what with windows and all, but doors are probably the most likely entry point for anyone attempting to access your home illegally.
By the same token, you should never open a door, or even unlock it, without knowing who is on the other side.
Thankfully, peepholes are not exactly new technology, but there have been a few improvements made to them over the years. In all cases, though, the important detail is to ensure you can see enough of the entryway that no one could be hiding off to the side or down low.
To begin with, you still have the traditional fish-eye peepholes everyone is probably familiar with. I would strongly recommend one that has a privacy cover; bizarrely enough, peephole reversers – devices that allow people on the outside of the door to look through your peephole – do exist. There are, of course, aftermarket covers if you already have a peephole. Bear in mind that your door has to be close to the intended thickness for the peephole, otherwise the image and viewing angle may be affected.
Moving on, but in a similar vein, there are screen-style peepholes as well. These require larger holes in your doors, but have the arguable benefit of being able to view them without putting your face right up against the door, as well as potentially a wider viewing angle. However, due to the projection nature of their image, they are much less effective at night unless you have a bright porch light.
Technology marches on, as it is wont to do, and now we also have door-mounted, battery-powered peephole cameras as available as well. There are no shortage of options, though most seem to be rebranded copies of the same Chinese hardware, but they can offer such things as motion-activated recording, night vision, a screen large enough to view from across the room, and so forth. These typically do not fall under my general admonition to avoid Internet-of-Things devices simply because they have no external connectivity.
Speaking of, there is no shortage of IoT devices who attempt to simplify looking out your front door, even from your couch or another state. Unfortunately – and consistently with the theme on this site – most of them have glaring security flaws. It is entirely possible to construct a significantly more-secure homebrew solution for having a camera overlooking your front door – as well as wherever else you want – but that is a whole separate post, if not series of posts.
Finally, a locking storm door does not improve the security of your home any, but it can give you a different – not necessarily better – way of determining who is at the door. The glass will still be fairly easy to break if someone wants in, but that will give you time to slam the normal door in their faces.
As a general rule, opening the door to someone you did not expect is not a good course of action, and especially not at night. It is entirely possible to carry on a conversation through a door, and until they can confirm who they are and why they are there that is what I would recommend. It may seem a little antisocial, but when criminals force their ways into homes with innocuous scams like asking to use a phone, precautions are warranted.