We used to have one that you could stick to a window with suction cups. I never noticed any bees around it. The only reason I finally took it down was because of all the hummingbird poop all over the siding of the house and on the porch under that window!
Teeny little poops add up! :)
Did you make your own liquid or did you buy some? I used to make it (forgotten how) but maybe, if you're using store bought, that's whats attracting your bees?