You are at the corner at nine in the evening. A car has pulled up to turn right across the crossing you are about to use. The driver’s head is turned left, watching for a gap in traffic. You stay on the kerb and wait for a look that never comes. Nothing about you has changed since this afternoon, except that you are now a dark shape on a dark street, and the person who is about to move is not looking at you.
The usual advice is to be brighter. Light clothing, a reflective strip, a torch in your hand. All worth doing. But at this particular moment it can still miss, because the thing going wrong is not only how much light comes off you. It is where the driver’s eyes are pointed.
Safe Crosswalk went on the App Store today. It is a free iPhone app that gives you one tap for that thirty-second problem, and this post is both its first write-up and a plain account of what it will not do for you. First, the limit: it does not make you safe. It makes you easier to notice. Keep making eye contact, and keep waiting until the car has actually stopped.
The driver is not failing to see you, they are looking elsewhere
A turning driver runs a two-step routine. They turn their head left to find a gap in traffic, then start moving right while still processing what they saw. On-road eye-tracking has found that in a large share of turns, the driver never looks at the crosswalk at all.
That changes what “be visible” means. Extra brightness helps if it lands in the part of the visual field the driver is actually using. The premise of this app is that a light which changes has a better chance of pulling a head round than a light which is only bright and still.
What happens when you tap it
The whole screen and the rear torch flash together, and a voice says “Crossing.” Tap anywhere and it stops. If you forget, it stops by itself after 45 seconds, so a phone cannot sit flashing in a pocket, draining the battery and heating the torch.
There is a second way in. Hold instead of tapping, and you get the urgent alert: sound is forced on, and it goes to full brightness. The urgent version changes the intensity and the words. It never changes the flash rate, for the reason in the next section.
That is the whole app. One button, one job.
Why it flashes slowly, and why it is dimmer at night
Two instincts about a warning light feel obvious and are both wrong. The app is built around that.
The first instinct is that faster is better. Flashing between 10 and 20 times a second is the range most likely to trigger a photosensitive seizure, and above about 5 times a second flicker starts causing eyestrain. So the rate is clamped in code to between 2 and 4 flashes per second, and nothing can lift it: not a stored setting, not a migration from an older version, not the urgent hold. Research also found that 1 and 4 flashes per second are detected equally well, while 4 reads as more urgent to a driver. So 4 is both the ceiling and the default. A first-run notice tells you the app flashes brightly and sends anyone sensitive to light to the sound-only mode.
The second instinct is that brighter is always better. Past a point, a bright warning source starts masking the low-contrast things a driver still needs to see, and at night it costs you your own dark adaptation as well. So peak output follows the conditions. Daylight and dusk run at 100 percent, night at 60, fog at 70. Each of those numbers has its reason written on the screen where you pick it, rather than sitting in a settings list as a bare slider.
One more detail that reads like a bug until you know why. The dim half of each flash drops to 10 percent instead of going fully dark. A light that vanishes completely is harder for a driver to place in space, and testing found that a full-to-dim pattern worked better than full-to-off.
Fog, glare, and why the light stays white
“Amber cuts through fog” is repeated often enough to sound settled. For this, it does not hold. Fog droplets are far larger than the wavelength of visible light, so they scatter all colours almost equally; the belief comes from applying the wrong physics. Amber does reduce glare a little, but the only way to get amber is to filter, and filtering costs output. A phone is already dim next to a headlamp. So the app keeps every bit of brightness it has and stays white.
Fog still gets its own level, at 70 percent, for the same reason high beams are useless in it. Push a bright source into fog and it scatters back into a glare ball instead of reaching anyone.
This is not a hypothetical case for us. The app exists because one of us kept crossing a foggy street in San Francisco where drivers turning right did not see people.
Light or sound is your call, and that is deliberate
The app has three modes: light only, light and sound, or sound only. It asks you to pick, and it does not try to be clever about it, because the one fact that decides the answer is a fact only you can see. Is the driver’s window down?
A sealed modern cabin cuts roughly 35 decibels. With the window up, your phone would need to be almost touching the glass to be heard, so light is the mode that works. With the window down, the same phone carries several metres and clears the noise inside a stopped car. No app can see a car window from inside your pocket. You can, from the kerb, in about half a second.
The conditions setting is the same kind of decision. iOS gives apps no ambient-light reading, and pulling the weather would mean a network call and your location, which are the two things this app is built never to need. So the clock supplies a first guess, which makes the common case zero taps, and you override it when the clock is wrong.
That refusal to guess is also why the privacy story is short. There is no account, no location, no analytics, no advertising identifier, and no networking code anywhere in the app, so there is nowhere for data to go. Three values live on your device: the mode you chose, your flash rate, and whether you have seen the first-run notice. Deleting the app removes them. It never opens a camera session or records audio; on iOS, switching the torch on does not need camera access.
What it does not do
It does not make you safe, and the app says that on its own first screen instead of putting it in a footnote. It is one more way to be noticed. A safety aid that raises your confidence more than your visibility is the one way this backfires, so it is worth being blunt: this is not a substitute for looking both ways, not a substitute for pedestrian right-of-way rules, and not a reason to cross anywhere other than where it is safe to cross. Keep making eye contact. Keep waiting until the car has actually stopped moving.
It is also not the fix. The fix is street design: daylighting, so parked cars stop hiding people near the corner; leading pedestrian intervals; turn calming; limits on right turns on red. If a crossing near you feels dangerous, reporting it to your city is worth more than anything we can ship. This app is what one person can carry into the gap those changes leave.
It is free, with no subscription, no in-app purchase and no ads. There is no catch, because there is no business model attached to it.
FAQ
How can I make drivers see me when I cross at night? Make yourself easier to notice, and keep doing the things that already work: make eye contact, and wait until the car has actually stopped. Safe Crosswalk, a free iPhone app from Studio AM, adds one tap that flashes your screen and rear torch together while a voice says “Crossing”. It makes you easier to notice. It does not make you safe.
Does Safe Crosswalk work when my phone is on silent? Yes. The spoken alert plays through the media channel, which ignores the ringer switch. You can also choose Light only if you want no sound at all, or Sound only if the flashing bothers you.
Is the flashing risky for people sensitive to light? The rate is clamped in code to between 2 and 4 flashes per second and cannot be raised, including by the urgent hold. That keeps it out of the 10 to 20 Hz band most likely to trigger a photosensitive seizure, and below the roughly 5 Hz point where flicker starts causing eyestrain. A first-run notice says the app flashes brightly and points anyone sensitive to the sound-only mode.
Why does it not use full brightness at night? Because past a point a bright warning light starts masking the low-contrast things a driver still needs to see, and at night it also costs you your own dark adaptation. Daylight and dusk run at full output, night at 60 percent, and fog at 70, where a bright source would scatter into a glare ball.
What does Safe Crosswalk cost, and what data does it collect? It is free, with no subscription, no in-app purchase and no advertising. It collects nothing, and it contains no networking code at all, so there is nowhere for data to go. Three settings are stored on your device: the alert mode you chose, your flash rate, and whether you have seen the first-run notice.
Does the app make it safe to cross? No, and the app says so on its own first screen. It is one more way to be noticed, not protection, and it is no substitute for looking, for pedestrian right-of-way rules, or for crossing where it is safe to cross. Keep making eye contact and keep waiting for the car to stop.