Acoustic cameras for finding air leaks - gimmick or genuinely useful?

I run one through my plant's maintenace department a couple times a year for air leak surveys, and I started hauling it home on weekends when a project got slow. My honest take: for a quiet house, the old methods are mostly fine, and I'd be careful promising yourself it'll pay for itself on drafts alone. Incense and a $10 infrared thermometer found everything I needed to know in my own place. Where the camera actually earned its keep at home was two spots. First, a whistle in a second floor wall that turned out to be a loose dryer vent joint inside the chase, something I could never get close enough to with a handheld detector. Second, tracing which window in a bay of four was the actual leaker, since they all felt drafty at the sill. The camera picked the right one in about thirty seconds, and the foam and caulk went where it mattered instead of everywhere. One caution from using these at work: they'll happily paint a blob on a noisy fan or a busy compressor, so in a house you want the HVAC off and the kids and dog out of the room or you're chasing ghosts. If you can get a borrowed unit through someone you know, that's the sweet spot. Buying one for household use only makes sense if you've got a big leaky shop building or rental units to walk through.

I'm on the other side of this one. I bought a used one off an auction site for about the cost of a decent cordless drill kit, and it's earned its shelf space in ways I didn't expect. The draft stuff was honestly the least of it. The best catch was a slow drip in a bathroom wall from a hairline crack in a shower valve, way before any stain showed up on the drywall. Running water behind a wall has a sound signature you can pick out even in a busy house, and there's no incense trick for that. It also found a failing bearing on my furnace blower months before it started squealing loud enough to hear, wich turned a 'replace the whole motor' call into a $15 bearing swap. That's the real value for me, not drafts. A quiet house is exactly where your ears get lazy because nothing seems wrong. On the rental question, I get why it makes sense on paper, but the whole point for me was having it the Tuesday night when the toilet fill valve starts hissing at 11pm. Every time I've delayed a purchase like this waiting for a 'good reason,' I ended up paying a trade to diagnose something I could've found myself in ten minutes. If you're even a little handy, owning beats borrowing.

The thing that made these make sense to me was borrowing one on a day when the weather wasn't cooperating. Calm mild days are the worst for finding drafts with anything, incense included, because there's barely any pressure difference across the envelope to drive the air. What worked instead was shutting the house up tight and running the big window fan on exhaust in one opening, which pulls the whole house slightly negative and makes even marginal leaks sing. With the camera that turned a maybe-someday diagnostic into somthing you can do on any random Tuesday, weather irrelevant. Has anyone here tried pairing a borrowed unit with that fan trick, since it seems like it would multiply what the thing can see?

The use case that sold me was actually rattles, not leaks. Had an annoying buzz somewhere in the ceiling that only showed up when the furnace blower kicked on high. Went around with a borrowed unit and the blob lit up right at a loose duct strap in the attic. woud've never found that by ear since the sound bounced all over the room. Curious if anyone's tried the cheap phone mic attachments that claim to do the same thing. Seems like the range and sensitivity on those would be way worse, but for odd jobs around the house maybe that's all a person needs?

Total beginner question here but when I saw one of these at a trade show last spring the demo guy held it up to a window and it still picked up noise from outside on the street. That got me thinking, could you just point it at your walls from inside on a windy day and skip the whole ladder thing? Like does the sound come through the drywall or does it only work if the leak is actually hissing on your side of it? My garage has a whistle when it gets windy and I've spent two winters poking around with a candle and never found it.

One use for these that hasn't come up yet is bearings. I maintain the equipment at a small cabinet shop and one of these flagged the blower motor on our dust collector about three weeks before it would've died. The ultrasonic reading on the bearing housing was climbing every time I checked it, so we greased it, ordered the motor, and swapped it during a slow Friday instead of losing a whole day mid-job. Now I do a quick pass on the dust collector and the air compressor every couple months and log the readings. For a homeowner it's the same trick: point it at your furnace blower or fridge compressor once in a while and if it's getting louder over time, that's your early warning before something seizes up.