Hi - I've just ordered a microchip sensor cat flap for my two kittens. So far they've been chased up an enormous oak tree twice in three nights (and rescued twice by dh/the decorator with extra long ladder!), scared rotten in their own house and had my 12 day old cat flap broken by the neighbour's bully of a cat!! Upon reading the 'bumpfh' carefully I note that another cat can get in if it's less than 4 seconds behind an 'authorised' cat - surely this means that another cat chasing yours could get in but then not get out? Has this ever happened to you and if so did you just take the opportunity to drench the intruder with water and then chuck it out? (sorry if this sounds harsh but my father suggested an air rifle so it would be getting off lightly!!)