Realise you probably don't want to do any more plumbing,
but,
a flow switch in the hot water feed to the shower can switch on the extractor,
and,
buy an extractor with an adjustable follow-on time you can 'tune' the extractor to the shower cabin/wet zone.
Realise you probably don't want to do any more plumbing,
but,
a flow switch in the hot water feed to the shower can switch on the extractor,
and,
buy an extractor with an adjustable follow-on time you can 'tune' the extractor to the shower cabin/wet zone.