A smoke alarm has to be placed where air from the room can circulate throught it, so they're nearly always on the ceiling or near the top of a wall. There is the possibility you might have a CO₂ detector that would be located low, but those aren't too common.

Looking for "lumps up high" will usually give you a clue about where your alarms are. About the only thing likely to look similar might be a doorbell "chime" box, some of which are about the same shape and similarly located.

If you can manage to be close to one of the lumps when it chirps, you probably will be able to tell when it's the right one.

If you don't find it, it should stop beeping at you in about a month, although the time is quite variable.

John