The idea, orchestrated by St George's Church, involves 23 businesses in the Frankwell area of Shrewsbury.
The church itself will unveil its own display on Christmas Eve.
Rev Tim Vasby-Burnie said: "There are two goals. One is to help celebrate and draw attention to the businesses we have in Frankwell.
"There is a wonderful sense of community, and we are very keen to encourage people to go along to them.
"The second goal is using Christmas carols to remember what Christmas is all about."
Each participating business has been allocated a different carol and then it is left up to them how they interpret it in their displays.
Some are bringing in various community groups to help create the displays, which remain a closely-guarded secret until they are revealed at 12pm each day.
"They are all a mystery to me as well as everyone else," said Rev Tim.
"I have been very impressed with the ones I have seen so far.
"There are clearly more than 23 businesses in Frankwell but hopefully no one feels left out.
"From a business point of view there are a lot of things in town so hopefully this will bring people out to Frankwell to see the displays."
It is hoped the window advent calendar could become an annual celebration, with different businesses having the chance to get involved.