Can inside lock button be purchased later ?

Currently, the inside lock button can only be purchased together with the entrance door.

When unlocking the door via the inside lock button with auto-lock function enabled, the door will lock by itself after being closed which might cause the user to be locked out from the house if operated without key on person. Due to this reason, we recommend using the product as a set with "keypad outside reader". Since the "keypad outside reader" can only be installed on special door, application of inside lock button will be limited to doors with "keypad outside reader" only. 
** "keypad outside reader" can only be purchased along with the door product and cannot be replaced with keypad-less outside reader at later time. 

We will pass on the demands for addition of the products post-purchase to the development team.
Thank you for your understanding.