We have had a magnetic cat flap for many years and had no problems
with stray cats coming into the house.  The type we have is where the
cat wears a magnet around her neck and the flap has a battery which
activates a switch when the magnet comes near, allowing the flap to
open to let the cat in.

Unfortunately our next door neighbours have now also installed a
magnetic cat flap and so their cat can come into our house as well.
She is an aggressive cat and ours is quite timid.  We are now having
problems with cat spray around the house - either from the neighbour's
cat or ours because she is so stressed out by the other cat coming in.

Is there a different type of magnetic/electronic cat flap we could get
which would recognise only our cat and keep the other cat out?

We live in New Zealand so would be looking for something available by
internet or mail order.  The one we have seems to be the only type on
the market here.

Hope you can help.

Liz D