The "Psycho" house on the Universal Studios lot is used for the house's exterior.
According to the TV Guide, the cast of "An Unlocked Window" were not given the final few pages of the script to safeguard its shocking ending.
Besides not being given the last few pages of the script until the final shoot, no one but a limited crew and the two actors involved in the final scene(s) were allowed on the set.
John Kerr and Cathie Merchant both died on the same day: 2nd February 2013. They also shared the same birthday: 15th November.
The story bears several parallels to the 1946 RKO film "The Spiral Staircase." In it, after an opening murder scene, almost the entire story unfolds in one evening, a dark and stormy night, and takes place in and around an old Gothic style house. There is a seriously ill person being medically cared for upstairs, an alcoholic cook in the kitchen, a household handyman who must go out in the night on an errand, and unbeknownst to all, a murderer right under the roof with everyone throughout the evening and not revealed until the closing moments.