Door viewers allow someone in the home to see outside of the home without having to open the door. This is a great way to get a view of who is visiting prior to allowing them in. There is a standard location for door viewers to be installed on a door. Craftsman style door may require a slight shift in placement in order to line up correction with the intermediate rail.
A standard door viewer sits 58″ from the bottom of the door slab. This is different than its height from the finished floor. Not every door unit uses the same sill, so by stating where the door viewer will be located in relation to the bottom of the door, there is more consistency in its placement.
In addition to the standard location, there is also the option of an ADA location. A door viewer installed at ADA height sits 48″ from the bottom of the slab.