Slugs like yeast. They can smell the yeast in beer from about half a metre (1.6 feet) away, so you need to place beer traps no more than a metre (3.3 feet) apart. Beer traps aren’t very effective, though. Studies with time-lapse cameras have shown that most slugs manage to drink from a beer trap without falling in.
The few that do topple in aren’t affected by the alcohol; fortifying a slug trap with extra alcohol doesn’t help and they work just as well using bakers’ yeast and sugar. Slugs die in beer traps because they fall in and drown, not because they get drunk.