Smoke detectors don’t respond to cigarette smoke, unless you cram one smoker per m² in a room and have them all smoke half a pack, with all windows shut.
I have seen indoor parties at flats with smoke detectors, which never went off, despite heavy smoking indoors. Meanwhile something burning on the stove set off the detector, as it should.
This is a good compromise. I understand cafés wanting to be able to have their guests smoke at the tables on the street, and frankly if someone is walking the street at night by himself i couldn’t care less whether he smokes as long as the remains are put in the trash.