It happened again a couple of nights ago. I woke up in the middle of the night to go to the bathroom. As I took care of business, something was nagging at me, but I was groggy enough that it didn’t quite rise to the level of a conscious concern. As I lay back down in bed, however, it finally pushed through the fog: I was hearing a quiet beeping sound. Some electronic device somewhere in the apartment wanted my attention.
Thus began the Beep Hunt.
It’s one of the more annoying tasks of the wired life. I have a lot of electronic gadgets, and many of them are smart enough to let me know when they need attention. But few of them do it well.
The first time it happened was 20 years ago, when a pager battery got critically low in the middle of the night. It freaked me out. I started awake with an adrenaline rush and ran out into the living room to track down the strange noise. I guess that’s an old animal reflex — a strange and unexpected noise in the night could be a threat, so I responded in full fight-or-flight mode, ready to defend my family against the mysterious intrusion.
(Some of you kids may not know this, so I should explain that a pager at that time was a special-purpose one-way communication receiver. It works kind of like those things some restaurants use to tell you when a table is ready, except over much longer ranges. Someone who wanted to talk to you would call a special number you had given them. A computer would answer, and they could punch in a phone number where they could be reached. The computer would then send out a radio message to your pager, telling you the number. This was before widespread inexpensive cellular service, so you’d have to find a land-line to call them back. These were one-way devices because without a cellular antenna network, the signals had to go out over a small number of dedicated commercial antennas which used 1000-Watt bursts to broadcast the page over hundreds of square miles. Nothing you’d want to keep in your pocket could generate enough power for a return signal.)
This beep wasn’t a bad one. It was a long oscillating beep that happened every few seconds. They aren’t always that easy.
As far as I know, your brain uses three basic factors to figure out where sounds are coming from. First, there’s the relative volume difference between the ears, which works best when the sound is coming from one side and the other ear is hidden from the source by your head.
Second, there’s the different arrival time of the sound at your ears. As with the volume difference, it doesn’t work so well with sounds that aren’t far to one side because the sounds arrive closer together.
Third, there’s the way the sound waves interact with the structure of your ears. Your ear will attenuate different frequencies of sound in different ways depending on the direction from which the sound strikes your ear. This works best when the sound is complex, consisting of many frequencies, each attenuated a little differently, such as the rustling noise of an animal creeping through bushes — which would often have been a life-or-death concern for our ancient ancestors.
(Modern video games use a mathematical model of the human ear to simulate this attenuation in order to give you better directional cues for sounds. Warning systems for fighter pilots use a similar mechanism to make the sound easier to distinguish.)
Your brain has to pick the beeping sound out of a cacophony of other noises — everything from outside traffic and air conditioning to the sound of blood flowing through your head — so it helps if the sound is loud. It also helps if there’s a lot of information for your brain to analyze, which means that longer or more repetitious sounds are easier to localize. It’s especially helpful if you can turn your head and change the way the sound strikes your ears.
Thus, the easiest sounds for your brain to localize are long, loud, complicated, and repeated frequently. Of course, the easiest sound for a cheap low-power electronic device to generate is a quiet beep at a single pure frequency, and it helps power consumption to keep the duty cycle low by using a short duration sound delivered at a long interval. In addition, I think many devices are designed to emit a discrete and unobtrusive sound, in order to be less annoying. Of course, that only makes it more annoying when you don’t know what’s beeping, and you have to hunt for it.
My procedure for finding a beep is tiresome but fairly straightforward. First I stand sideways in the hallway of our condo, very still, with my back to the bathroom, waiting for the beep. This maximizes the sound difference from either end of the hall. If it comes from my left, it’s either the kitchen or the living room. If it comes from my right, it’s either the bedroom or my office. If neither, it’s probably something in the bathroom behind me.
This last time, it came from the office/bedroom direction, so I move to stand still at that end of the hall, with my office to the left and my bedroom to the right. It was coming from the office. I walked in and stood between the two desks, and quickly figured out it was coming from the VPN phone I use for work. Now I was close enough that it actually sounded like it was coming from the phone, and the display said something about incoming voicemail. I hit a couple of buttons and the sound stopped. Despite the message, I had no voicemail.
(When I first walked in, I noticed two of our cats sitting by the phone. It could be that they were curious about the noise, but I suspect that one of them may have stepped on a button. It wouldn’t be the first time one of our cats was responsible for a disturbing noise in the night.)
This wasn’t a bad one. It probably took me less than a minute. The worst beep hunt I ever had was caused by a failing battery in a UPS that emitted a pure beeping tone for one second every hour. The tone was so pure and high-pitched (which also makes it hard to locate) that even standing a few feet away, I couldn’t be sure where it was coming from. I had to find it by relative volume in different locations, which is kind of hard to compare when the beeps are that far apart. It took days to figure it out.