Checking a phone in five minutes: ghost touch, a check-up, and sampling rate

A lot of phone checking happens in a hurry: in a shop, at a seller’s door, at a repair counter with the technician waiting. You have a few minutes, a phone that isn’t yours yet, and no way to install anything. That is what the touch screen test and the phone screen test have always been for. This release adds three things to them.

Ghost touch, counted

Ghost touch is the screen reporting touches nobody made. The old advice on our touch test was to take your hands off for ten seconds and watch for cells lighting up by themselves. That works if the fault is busy. It doesn’t if the phantom touches come every twenty seconds, or land under your thumb while you’re holding the phone.

The new ghost touch test does the waiting for you. Put the phone down on something flat and dry, press Start, and take your hands away. After a three-second countdown, so the tap that started it doesn’t count, it watches for 30 seconds, a minute or two minutes. Every touch the screen reports in that window gets counted and ringed where it landed. The screen stays awake while it watches, and two fingers can’t close it, because a phantom double touch must not end the test that is looking for one.

The result reads the count three ways. Zero is clean. One or two could be a sleeve, a drop of water or a hand that came back early, so the test asks for a rerun before you read anything into it. Three or more is ghost touch, and if most of them cluster at one edge or corner, the result says where. That is usually a crack, a lifting screen protector or a bad flex cable.

It also notes whether the phone was charging. A cheap or failing charger is the most common cause of ghost touch, so a run that finds touches while plugged in tells you to unplug and run it again. If you run it both ways in one visit, the result shows both counts side by side. Fourteen while charging and zero on battery is a charger problem, not a phone problem.

Nine checks, one list

The phone screen test used to be a list of links to five separate tests. It is now a check-up: nine checks in order, each one a tap.

1. Touch grid, painted to 100%, with the most fingers you could hold down at once.
2. Ghost touch, 30 seconds hands-off.
3. Dead pixels, nine solid colors.
4. Burn-in, on gray.
5. Refresh rate, measured.
6. Resolution, read from the screen.
7. Speaker: a sweep from low to high, then left and right on their own.
8. Microphone: three seconds recorded and played back.
9. Vibration: three buzzes.

Each step keeps whatever it measured and asks one question only the person holding the phone can answer. The refresh rate step measures 120 Hz, but only you know whether the box said 120. Anything can be skipped, and anything done can be redone.

At the end, the summary copies as plain text or as a link. Opening the link shows a read-only card of the results, so you can drop it into the chat where you’re negotiating, or keep it as a record of the phone’s state on the day you bought it. If the page reloads halfway through, because a back gesture misfired or the browser dropped the tab, the check-up picks up where it was.

It has limits worth knowing. A browser can’t read battery health, the camera’s focus, water damage indicators, or whether the phone is still tied to someone else’s account. On an iPhone it can’t buzz the motor either, so that step is skipped there; switch the phone to silent mode and feel for the buzz instead. Check those things by hand before you pay.

Touch sampling rate, and its limits

Phones advertise touch sampling at 240, 360 or 480 Hz: how many times a second the digitizer reports where your finger is. The touch screen test now has a pad that measures it. Drag one finger in fast circles and it times the reports.

There is a catch, and the readout is built around it. Browsers collect touch reports between screen refreshes and pass the extras along as a batch. Some browsers pass on the whole batch; others hand over one sample per refresh and drop the rest. In the second case the pad would measure your refresh rate, not your digitizer. When the number lands at or below the screen’s refresh rate, the panel says so instead of reporting it as the sensor’s rate.

Two more things can make an honest reading look low. Many phones only raise touch sampling inside games, so a phone sold at 480 Hz can read 240 in a browser and be working as designed. And sampling only runs while your finger is moving, so slow circles under-report.

The same pad is on the refresh rate test for mice. Move the mouse in quick circles and it reads the polling rate: 125 Hz for an office mouse, 1,000 for most gaming mice. Chrome and Edge pass every report through, so they give the truest reading.

What stays on the phone

Nothing in these checks is uploaded. The ghost touch count, the touch grid and the sampling rate are worked out in the tab. The check-up keeps its progress in the tab’s own storage, which the browser clears when the tab closes. The microphone step records into memory, plays it back and throws it away. A shared link carries the step results and the numbers they measured, written out so you can read them in the link itself, and nothing about the device. The privacy page has the full list of what this site stores.

Try it

Open the phone screen test on the phone you want to check and press Start. It takes about five minutes. The ghost touch test and the sampling rate pad are also on the touch screen test on their own.