“Semrush Sensor is red.” “MozCast is running hot.” If you follow SEO news, you have seen these phrases used as shorthand for “Google is changing something”. SERP volatility trackers are useful early-warning systems, but they are also widely misread. A high reading is not proof of an algorithm update, and a calm reading does not mean your site was unaffected.
Each tracker watches a fixed set of keywords, compares today’s results with yesterday’s, and turns the difference into a single number. The choices behind that number, such as which keywords, which country, which device and how change is measured, explain why tools often disagree.
This guide explains how the best-documented trackers work, what their limits are, and how to read several together alongside official sources and your own data.
Key Takeaways
- Volatility trackers measure how much a sample of search results changes from day to day; they do not see Google’s algorithms directly.
- Semrush says Sensor compares each keyword’s results with the previous day using Levenshtein distance as a basis, plus normalisation.
- MozCast tracks a hand-picked set of 1,000 keywords and expresses daily change as a temperature, with an average day around 70°F.
- Tools differ in keyword sets, locations and devices, so they can disagree. Agreement across several tools is stronger evidence.
- Always confirm with the Google Search Status Dashboard and your own Search Console data before acting.
How volatility trackers work in general
Almost every tracker follows the same basic recipe:
- Choose a keyword sample. A fixed set of queries, often grouped by industry.
- Collect results daily from a set location and device, usually the top 10 or top 20 organic results.
- Compare with the previous day. Measure how many URLs entered, left or changed position.
- Aggregate the per-keyword changes into one score for the day and per category.
- Compare with a baseline so readers can see whether today is unusual.
The details at each step change what the tool can see. A tracker sampling only US desktop results cannot tell you what happened in German mobile results.
The trackers compared
| Tool | What it reports | Published methodology details | Known limits |
|---|---|---|---|
| Semrush Sensor | Daily volatility score, by category, for mobile and desktop | Fixed keyword set checked daily; per-item comparison of today vs yesterday using Levenshtein distance as a basis, with normalisation (Semrush KB); Semrush describes tracking 20+ categories | Keyword sample is fixed and proprietary, so it may not reflect your niche (ClickMinded) |
| MozCast | Daily “temperature” in °F | Hand-picked set of 1,000 keywords, top 10 organic results, average change scaled to look like a temperature; an average day is about 70°F (Search Engine Roundtable, 2012) | Described by ClickMinded as US-only and desktop-weighted |
| Algoroo | Daily volatility bar chart with weekly winners and losers | Little public detail on when or how data is collected, according to a Salience comparison | Methodology is not transparent |
| Your own rank tracker | Position changes for your keywords | You choose keywords, locations and devices | Only covers what you track; small samples are noisy |
Many other volatility indexes exist, from rank-tracking platforms and data providers. Before relying on any of them, look for the same details: sample size, location, device, measurement method and update time. If those are not published, treat the score as indicative only.
How Semrush Sensor measures change
Semrush’s knowledge base explains its scoring briefly:
“We measure how much has changed in a day using Levenshtein distance (as a basis) and normalization.”
— Semrush Knowledge Base, How is the Sensor score calculated?
Levenshtein distance counts how many edits it takes to turn one list into another, so new URLs, lost URLs and reordering all add to the score. ClickMinded describes Sensor as measuring daily volatility on a 0 to 10 scale across industries and countries. The Semrush blog’s algorithm update timeline uses Sensor readings such as “Very High” to describe some updates, which is a fair use: it shows how much results moved, not why.
How MozCast measures change
When MozCast launched, Search Engine Roundtable described its method: it records the top 10 organic results for 1,000 keywords each day, measures how much each set changed, averages that across keywords and multiplies the result by a fixed number to produce a temperature. The headline reading is easy to grasp, but the details of the method may have evolved since 2012, so check Moz’s current documentation before relying on specifics.
Why tools disagree
- Different samples. One tool may weight finance and health queries; another may lean towards retail.
- Different locations and devices. US desktop data can be calm while mobile results elsewhere shift.
- Different measures. Counting URL changes, position changes and SERP feature changes gives different answers.
- SERP layout changes. New features, such as AI Overviews, can move organic positions without any ranking change.
- Tracking glitches. A data collection issue can create a false spike.
How to read volatility tools together: a practical routine
- Start with the official source. Check the Google Search Status Dashboard for an open ranking incident.
- Look at two or three trackers. Note whether they agree on the day and the size of the spike.
- Drill into your category. Use category-level views where the tool offers them.
- Check your own data. Compare Search Console clicks and impressions with the same weekdays a week earlier.
- Label it correctly. Without a dashboard entry, call it unconfirmed volatility.
- Do not act on a single day. Wait for a pattern before changing anything.
| Situation | Interpretation |
|---|---|
| Dashboard shows an update; trackers spike; your clicks change | Likely affected by the update; analyse once the rollout completes |
| Dashboard shows an update; trackers spike; your data is flat | Update probably not affecting your pages so far; keep monitoring |
| No dashboard entry; several trackers spike | Unconfirmed volatility; check your data and wait |
| No dashboard entry; one tracker spikes | Weak signal; possibly sample-specific or a glitch |
| Trackers calm; your clicks dropped | Look at your own site: technical issues, seasonality or competitors |
For what to do next, see what to do during an unconfirmed update, and for why reported volatility and real impact differ, rankings versus traffic in update impact.
Common mistakes
- Treating a spike as confirmation. Only Google can confirm an update.
- Comparing scores across tools. A 7 on one scale is not equivalent to 80°F on another.
- Ignoring your own data. Industry-wide volatility says little about your specific pages.
- Watching only one tool. Single-source readings are fragile.
- Assuming calm means safe. Trackers may not sample your niche or country.
If you are choosing tools for your own monitoring, our guides to rank tracking and free SEO tools can help, and our guide to confirmed and unconfirmed updates explains labelling. Our Search Status Dashboard guide covers the official side.
Related Guides
- Update-Proof SEO: A Strategy That Survives Algorithm Updates
- Core Updates vs Spam Updates vs System Updates: Key Differences
- Google's Ranking Systems Guide Explained, System by System
Frequently Asked Questions
What is SERP volatility?
It is how much search results change over a period, usually measured daily by comparing the results for a fixed set of keywords with the previous day.
Does a high Semrush Sensor score mean a Google update?
Not necessarily. It shows that results in its keyword sample changed a lot. Check the Search Status Dashboard to see if Google has confirmed an update.
How does MozCast calculate its temperature?
At launch, MozCast tracked the top 10 organic results for 1,000 keywords, measured daily change, averaged it and scaled it to look like a temperature, with an average day around 70°F.
Why do volatility tools show different results?
They use different keyword samples, locations, devices and measurement methods, so they see different slices of Google.
Which volatility tool is best?
There is no single best tool. Use two or three together, plus the Search Status Dashboard and your own Search Console data.
Conclusion: use trackers as smoke alarms, not verdicts
Volatility trackers are useful for noticing that something is happening. They cannot tell you what Google changed or whether your site was affected. Read several together, confirm with the dashboard, and let your own data decide.
Need help monitoring updates for your site? Our SEO services include update monitoring and reporting. Request a custom quote.
References
- Semrush Knowledge Base: How is the Sensor score calculated?
- Search Engine Roundtable: SEOmoz tries to automate Google update notifications with MozCast
- Salience: MozCast vs Algoroo
- ClickMinded: SEO Weather – Google algorithm volatility tools
- Semrush Blog: Google Algorithm Updates Timeline
- Google Search Status Dashboard
