He means (I assume) they are not that good at detecting movement, cats or no cats! Making them eveb less suitable for starting an entry exit timer,
esp. in a confined space like a hallway. Quite likely I imagine if the 'lead up' to it is less than 1-2 metres then you're stood behind it (imagining how its fitted)
its obviously then too late, next stop I guess would be a room where the alarm really will 'go off'.
I would strongly advise fitting a door contact myself, it's not like fitting it should be an issue if wireless.