Why We Built Wattson: Your Mac Forgets Which Apps Drain It
Ask your iPhone which apps drained the battery this week and Settings will show you, app by app, hour by hour. Ask your Mac the same question and you get… the Energy tab in Activity Monitor: a rolling average of roughly the last eight hours, gone forever the moment you reboot, with no way to export anything. iOS has had per-app energy history for a decade. The Mac never got it.
That gap annoyed us on one specific afternoon: a MacBook that had clearly worked hard overnight — fans, warm chassis, battery down — and no way to answer the simple question “what was it?” By the time you look, the evidence has averaged itself away.
So we built Wattson: a menu bar utility that records which apps consume energy on your Mac, keeps that history across reboots, and exports it as CSV or JSON.
The honest-numbers problem
Building this taught us why Apple probably never shipped it: per-app energy is genuinely hard to report honestly, and dishonest energy numbers are worse than none.
Three decisions came out of that:
Share of total, not fake watts. macOS exposes a per-process “Energy Impact” — a composite score, not a physical measurement. Pretending otherwise (“Chrome used 3.2 watt-hours”) would be fiction. Wattson leads with what the data can actually support: “Chrome was 38% of your Mac’s energy yesterday.” Where we do show an estimated watt figure, it’s labeled as the allocation it is.
Sampling, disclosed. Continuous energy metering would itself burn meaningful energy — the measuring tool is one of the more expensive processes on the system. Wattson samples 5 seconds out of every minute, and the interface says “sampled 5 s per minute” instead of implying exact accounting. The sampler shows up in Wattson’s own ranking like anything else — measured on our machine it came to roughly 0.15% of measured activity, the recording service itself to under 0.01% — so you can check the cost rather than take our word for it. An energy tracker that wastes energy would be a bad joke.
The short-lived bucket. Here’s the surprise nobody talks about: in our measurements, roughly a third of all system energy goes to processes that live for less than a few seconds — spawned helpers, indexers, preference daemons — born and gone between any two samples. Most tools silently redistribute that energy into the apps they can see, inflating every number. Wattson shows it as its own row: “Short-lived background processes.” When a third of the story is unattributable, saying so is the feature.
Why a niche app at all
Wattson won’t be for everyone. It’s for the person whose battery was mysteriously flat after a night in a backpack; the developer checking whether their own app behaves; the IT person who wants a CSV before deciding which software a fleet keeps. That’s a narrow audience — and that’s fine. Small, honest tools that do one thing properly are exactly the kind of software we like building (it’s the same reason WhereInMenu and WhereInClipHistory exist).
Everything that matters stays on your Mac: the database is local, your process list and measurements are never uploaded, and the export files are yours. Anonymous usage analytics and crash reporting exist behind a single switch in Settings that is off until you turn it on. Recording needs a one-time admin approval because that’s how macOS gates per-process energy data — the app explains it up front instead of burying it.
Wattson is free, installable with Homebrew, and the history is yours to keep — which is more than macOS ever offered.