According to our experiences, most of old doors can be changed to install scg digital door locks.  The following is the normal process:

First of all, the door thickness must reach 3.5cm for tubular latch locks and 4.5cm for US mortise locks. 

Second, we'll go to check the status of your old door locks at site, such as Mortise type, panel type, and size.  Or you can take pictures on your own and send them to us via e-mails to accelerate the process.