Where is the beeping coming from?? how long will it last?

there is a beeping noise, about every 30 seconds, coming from somewhere outside of my house. my roommate and i cannot tell where it is coming from, and since we live in a townhouse neighborhood in brooklyn, we can’t just ask the neighbors. we think it might be a smoke alarm with dying batteries, in which case i would like to know how long this will last. i cannot wear earplugs because they hurt my ears. i am sorta’ losing my mind over this.