It's 2am and a smoke detector with a dying battery chirps once a minute. You stand in the hallway trying to place it, but the sound bounces off every wall. Upstairs? The back bedroom? You have a handful of detectors and no idea which one is failing.
Follow the sound. ChirpHound turns your iPhone into a directional chirp-finder. It listens for that short, high-pitched beep and shows a live level meter that climbs as you close in. Walk room to room and watch the reading rise. When it peaks, you're standing under the culprit. It reads smoke and carbon-monoxide alarms, appliance end-of-cycle beeps, and other repeating tones the same way.
So instead of yanking batteries out of the wrong detectors and hoping, you follow the signal straight to the one that's failing, usually in a minute or two. Then you go back to bed.
ChirpHound is on the App Store. Next time something starts chirping in the dark, let your phone point the way.