Signaling for rescue at night: how far can a phone flashlight actually carry an SOS?
Been testing how usable a phone's LED flash actually is as a signal light compared to a real signal mirror or a dedicated strobe. Some notes:
The rule of 3 (3 flashes, pause, repeat) is easy to keep consistent with a phone since you can automate the timing instead of counting in your head while cold and tired, which is when you actually need this.
Battery draw is basically nothing for a flashing pattern over a few hours, way less than I expected, since the LED itself is the power draw, not the CPU.
Line of sight is still the hard limit, same as any handheld light. A phone flash is roughly comparable to a small keychain flashlight in output, so don't expect signal-mirror range in daylight. At night against a dark treeline it's a different story.
Morse SOS specifically (... --- ...) reads as intentional distress to anyone who recognizes the pattern, versus a random blinking light which people tend to dismiss as a bug or a phone notification.
I ended up building this into the app I'm working on (automated SOS/Morse via camera flash, works with screen off) mostly because I kept forgetting the correct timing myself in the field. Curious what others use for night signaling, chemical light stick, dedicated strobe, mirror, or just voice/whistle and skip light entirely?
Posted Jul 6, 2026, 8:57 PM UTC