Short answer: The fault that quietly ruins the picture is the one nobody inspects: a scratch or hairline crack on the small window over the rear lens. It is filed as cosmetic because a phone lives in a pocket, and it turns every bright object in the scene into a permanent smear of scattered light in the same place in every frame. The fault that actually retires phones is the front display, and that is the one this job cares least about — though not for the reason we used to give here: what a setup session needs is a live touch layer, not a readable screen, and we corrected that ourselves. Below is a triage table for every common fault, a five-minute inspection you can do before committing a handset, and an honest note about the line we have been repeating that skips all of this. Apps like Background Camera RemoteStream run with the display off, which is exactly why the front-glass question turns out to be the easy one.
Almost every article about reusing an old handset as a camera says some version of "any old phone will do." Almost every article about buying one says "check for damage." Neither one tells you which damage, and the two are not the same list. A fault that makes a phone useless in a pocket can be irrelevant on a bracket, and a fault that nobody would return a phone for can wreck a picture permanently.
Here is the triage I would actually run.
The fault that ends a phone's life is the one this job does not use
A phone gets retired for its display more than for anything else. It is the largest, most exposed, most expensive-to-repair part, and once it is unreadable the device is unusable as a phone. So the pile of candidate camera handsets is heavily weighted towards cracked fronts.
For this job that is close to the best possible news. A camera setup runs with the display off — that is the entire premise of leaving a phone recording for weeks — so the condition of the front glass stops mattering the moment setup is finished. What you need is:
- Enough of the touch layer alive to complete setup once — which is the binding requirement, not legibility.
- Nothing loose enough to fall out of the frame or short something.
That is it. Cracks, dead pixels, colour shifts, a dim backlight, burn-in from a previous life as a dashboard: none of them affect a single frame of recorded video, because none of them are in the optical path. The picture is made by a sensor behind a different piece of glass entirely.
There is one distinction inside this that matters more than the crack itself: broken glass and a dead touch layer are different faults. Spiderwebbed glass that still registers taps is fine. A panel that shows an image but ignores your finger, or a panel that is simply black, is a phone you cannot configure by hand — but it is not a dead end. A wired mouse through a USB-OTG adapter gives you a pointer: Android has supported USB host mode since 3.1, no drivers, and it works on a locked phone. We walked that through, case by case, in a separate piece on setting up a handset you cannot touch.
The piece of glass nobody inspects
Now the other side. There is a small protective window over the rear camera, and it takes exactly the same impacts as the rest of the device. When it chips, scratches or crazes, three things happen at once:
- Bright objects smear. Any strong light source in the scene — a bulb, a bright doorway, headlights turning in — gets scattered by the damage instead of passing cleanly through. You get a haze, a streak or a starburst radiating from that light.
- It happens in the same place every time. Unlike a smudge you can wipe, the damage is fixed relative to the sensor, so the artefact lands on the same part of the frame in every single frame, all day, for as long as the setup runs.
- Contrast falls across the whole image. Scattered light does not only make a streak; it lifts the dark parts of the picture towards grey, which is precisely where the detail you wanted was hiding.
None of this shows up in the way people usually check a phone. A quick snapshot in even indoor lighting can look completely normal. It shows up when there is a strong light in view, which describes most of the situations a camera is pointed at: a door onto daylight, a window, a driveway at dusk, a room with a lamp in the corner.
And crucially, nobody who later looks at that footage says "the lens window is chipped." They say the camera is bad.
Triage table
| Fault | Verdict for camera duty | Why |
|---|---|---|
| Cracked or shattered front glass, touch still works | Fine | Display is dark the whole time. Needs to survive one setup session. |
| Display black or touch layer dead | Workable | Not in the optical path. Setup runs off a wired mouse on a USB-OTG adapter, which works even on a locked phone. |
| Scratch, chip or crack on the rear camera window | Usually disqualifying | Permanent scattered light in a fixed place in every frame; kills contrast around any bright object. |
| Greasy or hazy rear window, no physical damage | Free to fix | A wipe. Do this before judging any picture, including one you are using to judge a phone you are buying. |
| Known water exposure in its history | Treat as unknown, not as a pass | Corrosion is slow and cannot be inspected from outside. It may run for years. It is not a device to put somewhere that matters and forget. |
| Battery will not hold a charge | Less decisive here than elsewhere | The device lives on a cable for this job. There is a lot written about phone batteries already and I am not going to re-run it here. |
| Missing SIM tray, no service, carrier-locked | Irrelevant | The network story for this setup is Wi-Fi. A handset with no service is still a computer with a camera in it. |
| Dead speaker or microphone | Depends entirely on whether you want sound | Silent video is a complete answer for many uses and useless for others. Decide before, not after. |
| Dead power button | Real nuisance | A device you cannot restart by hand is a device that needs a plan for the day it needs restarting. |
The five-minute inspection
1. Wipe the rear window with a soft cloth. Do this FIRST — half of
what looks like damage is a fingerprint from years in a pocket.
2. Hold the rear window at an angle under a bright light and rotate it.
Scratches are almost invisible face-on and obvious at a glancing angle.
3. Open any camera app and point it at a lit bulb from a few metres away,
with the rest of the room dim. Damage that hides in daylight is
unmissable here: streaks and haloes radiating from the light.
4. Take one frame of the actual scene you plan to watch, and look at it
on the largest screen you own — not on the phone. A phone display
flatters everything.
5. Only now check the front: can you read enough of it, and does it
respond to touch, to get through a setup once?
Step three is the whole test. If a phone passes step three, the rest of its cosmetic history is mostly irrelevant to this job.
An honest note about our own line
The line we have repeated more than any other is that the broken old phone somebody was told to recycle still films better than a cheap camera. I still think it is broadly right, and it is true of the specific break that put most of those phones out of service — the front one.
It is not true of all of them, and we have never said which. A phone with a chipped rear window will produce a worse picture than a cheap dedicated camera in exactly the situations you bought a camera for, and no software fixes it, ours included. Repeating a cheerful generalisation without the exception is how people end up disappointed by the right idea.
The exception is one sentence long and it belongs next to the claim every time it is made: check the small window, not the big one.
What this list deliberately does not settle
It does not tell you whether a given handset is fast enough, has enough storage, or will get warm where you want to put it. Those are real questions with real answers and they are not damage questions. This is only the triage for a device that has already been dropped, which is most of the devices anybody is considering for this.
It also cannot tell you about corrosion, board-level damage, or anything else that lives under the case. Nobody can, from the outside. The honest handling of that is not a confident verdict but a placement decision: a device with an unknown internal history goes somewhere you will notice it stopping, not somewhere you are relying on it silently for months.
What to do this week
If there is a retired handset in the house you have been meaning to put to work, do step one and step three above tonight. Five minutes with a cloth and a lamp will tell you whether you have a good camera or a permanently hazy one, and it will tell you before you have chosen a spot, run a cable and started trusting the thing.
More at superfunicular.com, and the app is Background Camera RemoteStream on Google Play.
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