How fast should Morse be signalled?

With one unit set near 90 milliseconds: a dit is 1 unit on, a dah is 3 units on, the gap inside a letter is 1 unit, between letters 3 units and between words 7 units. SOS lasts roughly five seconds including word gaps; speed matters far less than even, steady rhythm.

Does the screen flash actually work as a rescue signal?

At night or in low light, a bright full-screen flash can be seen for a surprising distance, especially from the air or across a valley. In daylight a signal mirror reflecting the sun is far stronger; sweep the horizon slowly and flash any aircraft you spot. The optional torch button uses the camera LED where the browser and hardware expose the torch constraint.

What do the ground-to-air letters V, X, N, Y and F mean?

Lay symbols at least 5–6 metres tall with strong contrast against the ground: V means need assistance, X means need medical assistance, N means No, Y means Yes, F means need food and water, and an arrow means proceed in this direction.

Should I carry a PLB or a satellite messenger?

A 406 MHz PLB sends a registered emergency burst to the COSPAS-SARSAT satellite network with no subscription, but it is one-way and emergency-only. A Garmin inReach or similar messenger offers two-way text and tracking but requires a subscription. A phone shows offline GPS position with no signal but cannot call — carry at least one real emergency device in remote terrain.

Signal mirror reflecting a sun beam across a mountain valley, with an orange whistle and survival blanket on rock

SOS & Morse Signal ToolkitSOS 求救信号工具

Live Morse encode/decode with sound and screen flash, plus whistle rules, ground-to-air symbols and emergency device guidance. 摩斯电码实时编解码、声音与屏幕闪光播放，附哨声规则、地对空标志与应急设备选择建议。

🧭 Weather & Navigation天气与导航求救 🆘 ITU International MorseITU 国际摩斯电码 📅 Updated Oct 20262026 年 10 月更新

How to signal SOS

When you cannot call for help, attention is everything. This toolkit turns any message into International Morse code and plays it as an audible tone and a full-screen white flash, so a rescuer — in a helicopter, across a valley or through a whistle blast — can read the same rhythm.

Morse encodes each letter as a pattern of short and long elements. SOS is three short, three long, three short — ··· −−− ··· (...---...) — chosen because the pattern is unmistakable, not because the letters abbreviate a phrase. Timing is expressed in units: a dit is 1 unit of light or sound, a dah is 3 units, the gap inside a letter is 1 unit, the gap between letters is 3 units, and the gap between words is 7 units. This player uses roughly 90 milliseconds per unit, so a complete SOS takes about five seconds; precise speed matters far less than an even, deliberate rhythm that does not blur the dits into the dahs.

Light, sound and the torch

At night the full-screen flash is visible surprisingly far, especially from the air. In daylight a signal mirror is dramatically stronger — any reflective surface works: dedicated mirror, phone screen, CD or polished knife blade. Reflect the sun and sweep the horizon slowly, flashing any aircraft you see even if it looks distant. A whistle carries farther than a shout and costs a fraction of the energy; whistle, shout, fire or flash in groups of three, evenly spaced, and listen for a two-signal acknowledgement. Where the browser and camera hardware support it, the Torch button drives the rear LED via the getUserMedia torch constraint; unsupported devices show a quiet “torch unavailable” message rather than failing.

Ground-to-air symbols and emergency devices

For a searching aircraft, build ground symbols at least 5–6 metres tall from anything with strong contrast — branches, clothing, rocks or footprints in snow: V need assistance, X need medical assistance, N no, Y yes, F need food or water, and an arrow means proceed in this direction. Three fires in a triangle are a recognized distress pattern; use green boughs for smoke by day and dry fuel for bright flame at night. Electronics are force multipliers: a 406 MHz PLB reaches the COSPAS-SARSAT satellite network without a subscription but is emergency-only and one-way; a satellite messenger adds two-way text and tracking for a monthly fee; a phone still displays offline GPS coordinates with no cell signal but cannot make a call. In remote terrain carry at least one device that can actually summon help.

如何发出 SOS 求救信号

打不出求救电话时，「被看见、被听见」就是一切。本工具把任意文字编成国际摩斯电码，并以蜂鸣声与全屏白闪同步播放——无论是直升机、山谷对面还是哨声，救援者都能读出同一个节奏。

摩斯电码用长短码元表示每个字母。SOS 是三短、三长、三短——··· −−− ···（即 ...---...），它被选中是因为这个组合极易辨认，而非任何单词的缩写。时序以时间单位计：点 1 个单位、划 3 个单位；字符内间隔 1、字符间间隔 3、单词间间隔 7。播放器每单位约 90 毫秒，完整 SOS 约 5 秒；绝对速度并不重要，关键是节奏均匀、从容，点与划不要糊在一起。

光、声音与手电筒

夜间全屏闪光的可见距离相当可观，空中视角尤其有效；白天则应改用信号镜——任何反光面都可以：专用信号镜、手机屏幕、CD、抛光刀面。反射阳光后缓慢扫过地平线，见到任何飞机（哪怕看似很远）都闪它。哨声比呼喊传得更远、耗能极低；哨声、呼喊、火光或闪光都以「三次一组、间隔均匀」发出，并留意是否有「两次一组」的确认回应。在浏览器与摄像头硬件支持时，手电筒按钮通过 getUserMedia 的 torch 约束驱动后置 LED；设备不支持时会安静提示「手电筒不可用」，绝不报错中断。

地对空标志与应急设备

面向搜救飞机时，用任何高对比物——树枝、衣物、石块、雪地脚印——摆出至少 5–6 米大的地面符号：V＝需要援助，X＝需要医疗援助，N＝否，Y＝是，F＝需要食物或水，箭头＝沿此方向前进。三堆火呈三角形是公认遇险标志：白天用青绿树枝生烟、夜间加干柴增强火光。电子设备是力量倍增器：406 MHz PLB 无需订阅即可接入 COSPAS-SARSAT 卫星网络，但只能单向应急；卫星通信器需月费，却能双向收发文字并共享轨迹；手机在无信号时仍能显示离线 GPS 坐标，却无法通话。去偏远地区，至少携带一件真正能叫到救援的设备。

Frequently asked questions常见问题

What is the Morse code for SOS?SOS 的摩斯电码是什么？

Three short, three long, three short: ··· −−− ··· (...---...). SOS is not an abbreviation — the pattern was chosen because it is unmistakable.三短、三长、三短：··· −−− ···（...---...）。SOS 并非任何短语的缩写，只是因为这个组合极易辨认。

How fast should I signal?发信号该多快？

At ~90 ms per unit: dit 1, dah 3, intra-letter gap 1, letter gap 3, word gap 7. SOS takes about five seconds — keep the rhythm even rather than fast.每单位约 90 ms：点 1、划 3、字符内 1、字符间 3、单词间 7。SOS 约五秒；宁慢勿乱，节奏均匀最重要。

Does screen flashing really work for rescue?屏幕闪光真的能用于求救吗？

At night a bright full-screen flash can be seen far away, particularly from aircraft. In daylight use a signal mirror or any shiny surface and sweep the horizon.夜间明亮的全屏闪光可在很远距离（尤其空中）被看到。白天请用信号镜或任何反光面缓慢扫过地平线。

What do V, X, N, Y and F mean on the ground?地面摆出的 V、X、N、Y、F 各代表什么？

Symbols at least 5–6 m across: V = assistance, X = medical help, N = No, Y = Yes, F = food/water, arrow = proceed this way.符号至少 5–6 米大：V＝需要援助，X＝需要医疗，N＝否，Y＝是，F＝需要食物/水，箭头＝沿此方向。

PLB or satellite messenger?PLB 和卫星通信器怎么选？

A 406 MHz PLB reaches the COSPAS-SARSAT satellite network with no subscription but is one-way and emergency-only; a messenger (inReach, Zolstar) is two-way with a subscription. A phone gives offline GPS but no calls without signal — carry at least one emergency device.406 MHz PLB 无需订阅即可接入 COSPAS-SARSAT 卫星网络，但仅限单向应急；通信器（inReach、Zolstar 等）双向但需订阅。手机无信号时只能离线定位、不能通话——至少带一件真正能呼救的设备。