Things that go beep in the night

Most carbon monoxide and smoke detectors have low-battery alert warnings. The device will beep periodically when its battery is low. Based on my experiences, they are apparently designed only to do this late at night, when you are asleep. So last night, once again, I was awakened to this annoying, periodic "blip" sound.

This time, it took me about 10 minutes just to figure out where the noise was coming from. (I'd forgotten the CO detector's whereabouts.) Combined with the period of about a minute between beeps, the nature of the sound made it hard to find. Though each beep was quite loud, it had no directionality -- it seemed to be coming from all around me, even from inside my head. In this state, I wandered into the hallway, then into the kitchen, then into the living room, where I finally realized what the sound was.

Later, my wife told me about something she'd read about analog telephones. The old phones with an actual ringing bell can be easier to locate across a space because the ringing sound is harmonically more complex. The human ear can usually latch onto it more easily than a modern electronic ringer because the harmonic content of the ring tone provides more clues that our brains know how to interpret to gauge distance and orientation. The electronic ringtones tend to be harmonically simplistic.

So, this CO alarm's beep, though loud enough, was difficult to place spatially because it was probably nothing more than a single frequency, with few overtones.