I have had and fitted many cat flaps through the years. It is pretty easy to do yourself and of all the them the best in so many ways has been the sureflap microchip cat. Most robust, easiest to fit and keeps other out. Has lasted more than three times as long as any other and was not three times the price.
We started off with a magnetic catflap (thing hung off cat's collar) but she kept losing it, so we had to leave the catflap open to all gentleman cat callers which was pretty disastrous. Finally bought the microchip cat flap and it's brilliant. No more mishaps and it warns you ages in advance if the battery is getting a bit low.
I just went for it with the jigsaw, the fit was pretty forgiving. I wasn't sure what the door was made of, it turned out to be 2 sheets of coated aluminium with foam inside and I got through that by drilling 4 corner holes and then jigsawing along between them from both sides. It took a bit of oomph and blunted the drill bit though! I think some wooden doors have metal strips running inside for security so you might find them when you start cutting it is the only thing that'd put me off a bit.
Cat1 and Cat2 are happy housemates but I am not spending the rest of my life opening and closing doors for them once Cat2 is cleared for outdoor missions.
So, solid wood looking back door. Top half double glazed, bottom seems just wood probably went in mid 90's with the original wooden double glazed windows. Do I need to get someone in to put a flap in, or can I attack it with a jigsaw and do it? Ie, is it hard to get it just right so it fits without howling gale drafts, or are they a bit forgiving on the fit?
And - high tech or low tech? I know the microchip ones are pricier but obviously it's useful to not become the neighbourhood hangout for all felines (that's currently our summerhouse) and it would help if Cat2's likely attempt to take over the neighbourhood meets any resistance.
But, are there any downsides to the micro ones? Can you turn it off and use it just as a normal flap? If we go away on holiday it won't suddenly quit working and trap them outside? Can they get stuck?