@mhoye It took me embarrassingly long to realize that a stopwatch lap timer is much better than a human attention span at predicting the next smoke alarm low-battery chirp, even if the inter-chirp timing is a little irregular.
(My other opinions: this task is much easier with more technology—stepstool, chunky over-ear headphones, and bisect search for the location. Oh, and don't buy Kidde. Kidde sucks because it's screamier and more prone to false alarms.)