And remember that indoor/outdoor cats can also fall from upstairs windows so be careful about opening those when cats are around.
We have always suffered this problem - but only when we re-homed out 2nd cat - during the hottest July - and having to have the patio door shut was a nightmare!
Anyway, we have had to put 'barriers' up the windows to stop the cats getting out - the more nicer looking one are the venition blinds in the bedroom (as they cant work out how to get behind them, plus the pvc windows we have there is a latch at the bottom which we hook the blinds into).
The other upstairs windows (study & bathroom) havent got v.blinds up as we coudlnt afford them - so we bought some expanding trellis from Homebase and put some of the sticky clips on the window frame, expanded the trellis, clipped it in place and that is our 'budget' solution to not having cats escape.
We full well know that our cats can get out as we wondered one day why one of our cats (the more inquizative one) was outside, when neither of us had let him out. He'd only gone out of the study window (this was prior to the trellis), jumped onto the porch and then onto the pavement below!
We do rent our house and the chap who did the inspections did ask us 'so is this to keep them in or out then' jokingly!
