1. Get ready before you head out
Open Options with an internet connection and wait for Ready offline. Install it for easy access, then close and reopen it in airplane mode to check that it works. Browser storage can be cleared or evicted, so check before every trip.
New versions download in the background and reload Tracer automatically when ready. This stops the camera and clears any unsaved paused frame. Your color settings are kept.
2. Find a comfortable highlight
Try the practice scene and switch between cyan, yellow, and white. Use Split view to compare with the original. The scene contains simulated red marks, not real blood.
3. Adjust to your surroundings
Start with Red and lower sensitivity. Increase it gradually, or use Dark red for a wider range of muted red-brown tones. Pick lets you tap a visible color to match. Shadows, drying, surfaces, and lighting can all change what is highlighted.
4. Use your camera
Allow camera access when asked. Use natural light when possible, hold steady, and scan slowly. The flashlight button is available only when your browser and camera support it. Pause releases the camera and flashlight while keeping the last frame for adjustments or saving. Resume restarts the camera. Stop releases the camera and clears the view.
Understand the limits
This is a color filter, not a way to identify blood or rule it out. It can highlight leaves, soil, clothing, and other objects. It can miss blood, especially in poor light. Keep looking at your surroundings directly and stop moving before using the screen.
Private by design
Camera frames stay in this browser. There are no accounts, analytics, uploads, or location requests. Settings are saved locally. Images are saved only when you choose Save view. Stop camera releases the camera; switching apps also stops it.
Camera troubleshooting
Use HTTPS (or localhost for development), allow camera permission in browser settings, and close other apps using the camera. On iPhone, open in Safari if an in-app browser cannot access the camera.