Method 1 — accelerometer apps (contact)
Most vibration apps on the App Store use the motion sensor already inside the phone. You press or rest the phone against a surface, and the app charts the movement the sensor feels — usually as a waveform, a spectrum, or a single running level.
That approach is legitimately useful for slow, large-scale motion: floor and balcony sway, structural movement, a rough look at whole-machine shake. Because it doesn't use the camera, it also works in the dark.
The honest limit is sample rate. The iPhone delivers motion-sensor data to apps at a rate that caps reliable frequency readings somewhere around 15–50 Hz, depending on the model and the app's processing. Most machine problems live above that: a standard 3,600 RPM motor runs at 60 Hz — already out of reach. Getting higher on a phone means buying an external USB accelerometer, which typically starts north of $300.
The second limit is contact. The reading describes wherever the phone is touching — nothing else — and holding a phone against running machinery is somewhere between awkward and a genuinely bad idea. Never strap or tape a phone to operating equipment.
Method 2 — the camera (non-contact)
The second way ignores the motion sensor entirely: record the machine with high-frame-rate video and measure how the image itself oscillates. Vibrating parts shift by fractions of a pixel from frame to frame, and that shift repeats at the vibration frequency.
The sampling math is the same as any digitizer — the Nyquist limit: to resolve a frequency, you must sample at more than twice it. An iPhone capturing 240 fps can therefore see periodic motion up to a theoretical 120 Hz; in practice, about 115 Hz is the honest ceiling, equivalent to roughly 6,900 RPM. That covers the common motor speed classes — 1,800 RPM is 30 Hz, 3,600 RPM is 60 Hz — plus fans, blowers, pumps, and most shop machinery.
The camera also does something a contact sensor can't: it measures everywhere in the frame at once, so it can show which part is vibrating, not just confirm that something is. The tradeoffs run the other way — the camera needs light on the target and a visible edge or texture to track, and it reads nothing in darkness.
Side by side
Accelerometer app — contact
- Senses with: the phone's internal motion sensor, phone touching the surface
- Reliable range: roughly 15–50 Hz on internal sensors
- Shows location? No — one reading for wherever the phone sits
- Darkness: works fine; no light needed
- Going higher: external USB accelerometer, typically $300+
Camera measurement — non-contact
- Senses with: high-frame-rate video, up to 240 fps
- Reliable range: about 8–115 Hz (≈480–6,900 RPM)
- Shows location? Yes — everywhere in the frame at once
- Darkness: no — light is signal; dim scenes fail
- Distance: measures from across the room; nothing touches the machine
What neither method gives you
Neither an accelerometer app nor a camera measurement gives you calibrated amplitude — no mm/s, no mils, no go/no-go verdict. Phone sensors and cameras are not calibrated instruments, and any app that renders a severity judgment from them is guessing. Frequency is the phone's honest lane: it's a counting measurement, not an amplitude one. If the decision is safety-critical — acceptance testing, a warranty dispute, anything where being wrong costs real money — bring in a qualified technician with a calibrated contact instrument.
How VibraLens does the camera method
VibraLens implements the camera approach as an instrument rather than a slow-motion trick. Point the iPhone at a running machine and it records at up to 240 fps, paints a color overlay wherever it finds periodic vibration — hue mapped to frequency on a fixed 0–120 Hz legend — and reads out the dominant frequency in hertz, live. Recordings save with the legend and readout burned in, so a reading becomes evidence you can share. Everything runs on-device: no account, no uploads, no network access at all. It's $4.99 once — no subscription.
Technique matters more than gear:
- Brace the phone on a rail, tripod, or doorframe — handheld tremor shows up below about 20 Hz.
- Aim at a textured spot on the housing — labels, bolts, seams — not at spinning blades or belts.
- Add light or use the built-in torch; light is signal.
- Self-test first: an electric toothbrush should read about 75–80 Hz from a foot away. If it does, your technique is good.
The same honest limits apply: an ~8–115 Hz reliable band, no reading in darkness, no amplitude or severity — and it never replaces a calibrated contact instrument or a certified inspection. See what it reads and what it doesn't.
Quick answers
Can an iPhone really measure vibration frequency? Yes, within stated limits. The internal accelerometer handles slow structural motion up to roughly 15–50 Hz with the phone touching the surface. The camera at 240 fps handles about 8–115 Hz from a distance. Both measure frequency honestly; neither measures calibrated amplitude.
What's the highest frequency an iPhone can measure? About 115 Hz, using the camera at 240 fps — the Nyquist limit of the frame rate, minus margin. Internal-sensor apps top out far lower. Above ~115 Hz (roughly 6,900 RPM), you need dedicated external hardware.
Do vibration apps show severity in mm/s? Not credibly. Severity units like mm/s or mils require a calibrated sensor with a known mounting. Phone apps — accelerometer or camera — can tell you the frequency and, for the camera, the location, but not how bad the vibration is. For go/no-go decisions, use a calibrated contact instrument. More in the FAQ.