As always, remember that you cannot cut tempered glass! If you wish to install this pet door in a tempered glass window or sliding glass door, you should engage a glazier to replace the original glass with a new piece that includes the circular hole required.

However, the CatMate 255 has an unusually wide "self-framing" dimension of 2". So it easily installs in a dual-pane, insulated patio sliding door (again, with the help of a glazier).

Unlike a "magnetic" cat flap, the Cat Mate 255 is "electromagnetic". So the magnet doesn't actually unlock the flap; it provides a magnetic field which the door can sense electronically. The practical benefit of this design is that the sensing of the magnet can be from a greater distance. It does not have to actually touch the sensor.

On the other hand, the electromagnetic design requires power so a 9 volt battery is needed for the door itself.

A "four-way" lock is included which allows the cat door to be set to "in-only", "out-only", "in and out" and "locked". When the door is locked or set for out only, the cat cannot enter even though she wears the collar key.

Two magnetic collar keys are provided. These are the same as provided for the Cat Mate 254 and 256 electromagnetic cat doors.

Cat Mate 255 Electromagnetic
Glass Fitting Cat Flap