Every exterior door should have a peephole to look through. This seems obvious but apparently it is not. And the peepholes should be set at a height where they can be used. Sometimes this is a problem for smaller people since, when there are peepholes, they seem to have been installed for use by persons whose eyes are at least 5’6″ above the ground. This means that, if you are less than about 5’9″ or 5’10” you have to get up on your toes to look out the peephole. That’s ridiculous! Peepholes should be installed at a convenient height so they can be used. Obviously this depends on how tall you are but I would suggest about 5′ off the ground (about 6″ lower than the height of the shortest adult in your house) is about right.
If you don’t have a peephole in all your exterior doors, they are easy to buy and install. If I recall correctly, most hardware stores carry them and they come with a book of directions on how to install them. Usually all you need is a 3/4″ or 1″ drill bit and they fit right in to the hole.
And don’t forget–*all* exterior doors should have them, not just your front door. Otherwise, what if someone comes to the back/side door?