A novel pet door apparatus

An apartment pet door apparatus, comprising:

• a first panel;
• a flap within the first panel;
• a second panel coupled to the first panel by a first attachment mechanism;
• a third panel coupled to the second panel by a second attachment mechanism;
• wherein the point of coupling between the second panel and the third panel is adjustable to extend the length of the assembled unit;
• wherein the coupling between the first panel and the second panel and the coupling between the second panel and the third panel forms an assembled unit.

A system, comprising:

• a slidable door frame, comprising:
• a set of tracks comprising a first track at a top portion of the slidable door frame and a second track at a bottom portion of the slidable door frame;
• and
• an apartment pet door apparatus, comprising:
• a plurality of panels;
• a flap within one of the panels;
• wherein the plurality of panels are coupled to each other by at least one attachment mechanism;
• wherein the coupling between the first panel and the second panel and the coupling between the second panel and the third panel forms an assembled unit;
• wherein the point of coupling between at least two of the panels is adjustable to extend the length of the assembled unit;
• wherein an end of one of the panels is fitted within the first track of the slidable door frame and an end of one of the other panels is fitted within the second track of the slidable door frame.