It's my girlfriend's birthday...?

I want to surprise her when she comes home from work and have candles going up her stairs through her kitchen and onto her balcony with a bottle of champagne and cake waiting. There will be 20-25 small candles in her apartment and I'm afraid the fire alarm will go off bc of the smoke. Her place is pretty big--about 600 square feet. Anyone think the fire alarm won't go off if I space them out enough? Or any other ideas to lead her into the balcony? I would say rose petals (which there probably will be in addition to whatever I have), but I want to have some source of lights besides the overhead...Thanks for your input!